diff --git a/src/PhpSpreadsheet/Style/Color.php b/src/PhpSpreadsheet/Style/Color.php
index 3c002b270..282defc0c 100644
--- a/src/PhpSpreadsheet/Style/Color.php
+++ b/src/PhpSpreadsheet/Style/Color.php
@@ -362,23 +362,8 @@ class Color extends Supervisor
         $green = self::getGreen($hexColourValue, false);
         /** @var int $blue */
         $blue = self::getBlue($hexColourValue, false);
-        if ($adjustPercentage > 0) {
-            $red += (255 - $red) * $adjustPercentage;
-            $green += (255 - $green) * $adjustPercentage;
-            $blue += (255 - $blue) * $adjustPercentage;
-        } else {
-            $red += $red * $adjustPercentage;
-            $green += $green * $adjustPercentage;
-            $blue += $blue * $adjustPercentage;
-        }
 
-        $rgb = strtoupper(
-            str_pad(dechex((int) $red), 2, '0', 0) .
-            str_pad(dechex((int) $green), 2, '0', 0) .
-            str_pad(dechex((int) $blue), 2, '0', 0)
-        );
-
-        return (($rgba) ? 'FF' : '') . $rgb;
+        return (($rgba) ? 'FF' : '') . RgbTint::rgbAndTintToRgb($red, $green, $blue, $adjustPercentage);
     }
 
     /**
diff --git a/src/PhpSpreadsheet/Style/RgbTint.php b/src/PhpSpreadsheet/Style/RgbTint.php
new file mode 100644
index 000000000..582ae4839
--- /dev/null
+++ b/src/PhpSpreadsheet/Style/RgbTint.php
@@ -0,0 +1,175 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheet\Style;
+
+/**
+ * Class to handle tint applied to color.
+ * Code borrows heavily from some Python projects.
+ *
+ * @see https://docs.python.org/3/library/colorsys.html
+ * @see https://gist.github.com/Mike-Honey/b36e651e9a7f1d2e1d60ce1c63b9b633
+ */
+class RgbTint
+{
+    private const ONE_THIRD = 1.0 / 3.0;
+    private const ONE_SIXTH = 1.0 / 6.0;
+    private const TWO_THIRD = 2.0 / 3.0;
+    private const RGBMAX = 255.0;
+    /**
+     * MS excel's tint function expects that HLS is base 240.
+     *
+     * @see https://social.msdn.microsoft.com/Forums/en-US/e9d8c136-6d62-4098-9b1b-dac786149f43/excel-color-tint-algorithm-incorrect?forum=os_binaryfile#d3c2ac95-52e0-476b-86f1-e2a697f24969
+     */
+    private const HLSMAX = 240.0;
+
+    /**
+     * Convert red/green/blue to hue/luminance/saturation.
+     *
+     * @param float $red 0.0 through 1.0
+     * @param float $green 0.0 through 1.0
+     * @param float $blue 0.0 through 1.0
+     *
+     * @return float[]
+     */
+    private static function rgbToHls(float $red, float $green, float $blue): array
+    {
+        $maxc = max($red, $green, $blue);
+        $minc = min($red, $green, $blue);
+        $luminance = ($minc + $maxc) / 2.0;
+        if ($minc === $maxc) {
+            return [0.0, $luminance, 0.0];
+        }
+        $maxMinusMin = $maxc - $minc;
+        if ($luminance <= 0.5) {
+            $s = $maxMinusMin / ($maxc + $minc);
+        } else {
+            $s = $maxMinusMin / (2.0 - $maxc - $minc);
+        }
+        $rc = ($maxc - $red) / $maxMinusMin;
+        $gc = ($maxc - $green) / $maxMinusMin;
+        $bc = ($maxc - $blue) / $maxMinusMin;
+        if ($red === $maxc) {
+            $h = $bc - $gc;
+        } elseif ($green === $maxc) {
+            $h = 2.0 + $rc - $bc;
+        } else {
+            $h = 4.0 + $gc - $rc;
+        }
+        $h = self::positiveDecimalPart($h / 6.0);
+
+        return [$h, $luminance, $s];
+    }
+
+    /** @var mixed */
+    private static $scrutinizerZeroPointZero = 0.0;
+
+    /**
+     * Convert hue/luminance/saturation to red/green/blue.
+     *
+     * @param float $hue 0.0 through 1.0
+     * @param float $luminance 0.0 through 1.0
+     * @param float $saturation 0.0 through 1.0
+     *
+     * @return float[]
+     */
+    private static function hlsToRgb($hue, $luminance, $saturation): array
+    {
+        if ($saturation === self::$scrutinizerZeroPointZero) {
+            return [$luminance, $luminance, $luminance];
+        }
+        if ($luminance <= 0.5) {
+            $m2 = $luminance * (1.0 + $saturation);
+        } else {
+            $m2 = $luminance + $saturation - ($luminance * $saturation);
+        }
+        $m1 = 2.0 * $luminance - $m2;
+
+        return [
+            self::vFunction($m1, $m2, $hue + self::ONE_THIRD),
+            self::vFunction($m1, $m2, $hue),
+            self::vFunction($m1, $m2, $hue - self::ONE_THIRD),
+        ];
+    }
+
+    private static function vFunction(float $m1, float $m2, float $hue): float
+    {
+        $hue = self::positiveDecimalPart($hue);
+        if ($hue < self::ONE_SIXTH) {
+            return $m1 + ($m2 - $m1) * $hue * 6.0;
+        }
+        if ($hue < 0.5) {
+            return $m2;
+        }
+        if ($hue < self::TWO_THIRD) {
+            return $m1 + ($m2 - $m1) * (self::TWO_THIRD - $hue) * 6.0;
+        }
+
+        return $m1;
+    }
+
+    private static function positiveDecimalPart(float $hue): float
+    {
+        $hue = fmod($hue, 1.0);
+
+        return ($hue >= 0.0) ? $hue : (1.0 + $hue);
+    }
+
+    /**
+     * Convert red/green/blue to HLSMAX-based hue/luminance/saturation.
+     *
+     * @return int[]
+     */
+    private static function rgbToMsHls(int $red, int $green, int $blue): array
+    {
+        $red01 = $red / self::RGBMAX;
+        $green01 = $green / self::RGBMAX;
+        $blue01 = $blue / self::RGBMAX;
+        [$hue, $luminance, $saturation] = self::rgbToHls($red01, $green01, $blue01);
+
+        return [
+            (int) round($hue * self::HLSMAX),
+            (int) round($luminance * self::HLSMAX),
+            (int) round($saturation * self::HLSMAX),
+        ];
+    }
+
+    /**
+     * Converts HLSMAX based HLS values to rgb values in the range (0,1).
+     *
+     * @return float[]
+     */
+    private static function msHlsToRgb(int $hue, int $lightness, int $saturation): array
+    {
+        return self::hlsToRgb($hue / self::HLSMAX, $lightness / self::HLSMAX, $saturation / self::HLSMAX);
+    }
+
+    /**
+     * Tints HLSMAX based luminance.
+     *
+     * @see http://ciintelligence.blogspot.co.uk/2012/02/converting-excel-theme-color-and-tint.html
+     */
+    private static function tintLuminance(float $tint, float $luminance): int
+    {
+        if ($tint < 0) {
+            return (int) round($luminance * (1.0 + $tint));
+        }
+
+        return (int) round($luminance * (1.0 - $tint) + (self::HLSMAX - self::HLSMAX * (1.0 - $tint)));
+    }
+
+    /**
+     * Return result of tinting supplied rgb as 6 hex digits.
+     */
+    public static function rgbAndTintToRgb(int $red, int $green, int $blue, float $tint): string
+    {
+        [$hue, $luminance, $saturation] = self::rgbToMsHls($red, $green, $blue);
+        [$red, $green, $blue] = self::msHlsToRgb($hue, self::tintLuminance($tint, $luminance), $saturation);
+
+        return sprintf(
+            '%02X%02X%02X',
+            (int) round($red * self::RGBMAX),
+            (int) round($green * self::RGBMAX),
+            (int) round($blue * self::RGBMAX)
+        );
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2387Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2387Test.php
index 870ea6ab0..7e59418ad 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2387Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2387Test.php
@@ -15,7 +15,11 @@ class Issue2387Test extends TestCase
         $reader = IOFactory::createReader('Xlsx');
         $spreadsheet = $reader->load($filename);
         $sheet = $spreadsheet->getActiveSheet();
-        self::assertSame('335593', $sheet->getCell('B2')->getStyle()->getFont()->getColor()->getRgb());
+        // Font color being tested uses theme color with tint.
+        // Excel shows final color as 305496.
+        $expectedColor = '305496';
+        $calculatedColor = $sheet->getCell('B2')->getStyle()->getFont()->getColor()->getRgb();
+        self::assertSame($expectedColor, RgbTintTest::compareColors($calculatedColor, $expectedColor));
         self::assertSame(Fill::FILL_NONE, $sheet->getCell('B2')->getStyle()->getFill()->getFillType());
         self::assertSame('FFFFFF', $sheet->getCell('C2')->getStyle()->getFont()->getColor()->getRgb());
         self::assertSame('000000', $sheet->getCell('C2')->getStyle()->getFill()->getStartColor()->getRgb());
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/RgbTintTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/RgbTintTest.php
new file mode 100644
index 000000000..96e2003bc
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/RgbTintTest.php
@@ -0,0 +1,50 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
+
+use PhpOffice\PhpSpreadsheet\IOFactory;
+use PHPUnit\Framework\TestCase;
+
+class RgbTintTest extends TestCase
+{
+    public static function compareColors(string $style, string $text): string
+    {
+        $styleRed = hexdec(substr($style, 0, 2));
+        $styleGreen = hexdec(substr($style, 2, 2));
+        $styleBlue = hexdec(substr($style, 4, 2));
+        $textRed = hexdec(substr($text, 0, 2));
+        $textGreen = hexdec(substr($text, 2, 2));
+        $textBlue = hexdec(substr($text, 4, 2));
+        $maxDiff = 3;
+        if (abs($styleRed - $textRed) > $maxDiff) {
+            return $style;
+        }
+        if (abs($styleGreen - $textGreen) > $maxDiff) {
+            return $style;
+        }
+        if (abs($styleBlue - $textBlue) > $maxDiff) {
+            return $style;
+        }
+
+        return $text;
+    }
+
+    public function testRgbTint(): void
+    {
+        $filename = 'tests/data/Reader/XLSX/RgbTint.xlsx';
+        $reader = IOFactory::createReader('Xlsx');
+        $spreadsheet = $reader->load($filename);
+        $sheet = $spreadsheet->getActiveSheet();
+        $row = 0;
+        while (true) {
+            ++$row;
+            $text = (string) $sheet->getCell("B$row");
+            if ($text === '') {
+                break;
+            }
+            $style = $sheet->getStyle("A$row")->getFill()->getStartColor()->getRgb();
+            self::assertSame($text, self::compareColors($style, $text), "row $row");
+        }
+        $spreadsheet->disconnectWorksheets();
+    }
+}
diff --git a/tests/data/Reader/XLSX/RgbTint.xlsx b/tests/data/Reader/XLSX/RgbTint.xlsx
new file mode 100644
index 000000000..0ef26da69
Binary files /dev/null and b/tests/data/Reader/XLSX/RgbTint.xlsx differ
diff --git a/tests/data/Style/Color/ColorChangeBrightness.php b/tests/data/Style/Color/ColorChangeBrightness.php
index 8ddf188da..1c552e157 100644
--- a/tests/data/Style/Color/ColorChangeBrightness.php
+++ b/tests/data/Style/Color/ColorChangeBrightness.php
@@ -9,7 +9,7 @@ return [
     ],
     // RGBA
     [
-        'FF99A8B7',
+        'FF92A8BE',
         'FFAABBCC',
         -0.1,
     ],
@@ -20,17 +20,17 @@ return [
         0.1,
     ],
     [
-        '99A8B7',
+        '92A8BE',
         'AABBCC',
         -0.1,
     ],
     [
-        'FF1919',
+        'FF1A1A',
         'FF0000',
         0.1,
     ],
     [
-        'E50000',
+        'E60000',
         'FF0000',
         -0.1,
     ],
@@ -40,7 +40,7 @@ return [
         0.1,
     ],
     [
-        'E57373',
+        'FF5959',
         'FF8080',
         -0.1,
     ],
@@ -50,7 +50,7 @@ return [
         0.15,
     ],
     [
-        'D80000',
+        'D90000',
         'FF0000',
         -0.15,
     ],
@@ -60,18 +60,23 @@ return [
         0.15,
     ],
     [
-        'D86C6C',
+        'FF4646',
         'FF8080',
         -0.15,
     ],
     [
-        'FFF783',
+        'FFF984',
         'FFF008',
         0.5,
     ],
     [
-        '7F7804',
+        '847D00',
         'FFF008',
         -0.5,
     ],
+    'issue 3550' => [
+        '558ED5',
+        '1F497D',
+        0.39997558519241921,
+    ],
 ];