diff --git a/CHANGELOG.md b/CHANGELOG.md
index a92ad218..3cae9f51 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -45,6 +45,7 @@ Please also have a look at our
 
 ### Fixed
 
+- Don't render `rgb` colors with percentage values using hex notation (#803)
 - Parse `@font-face` `src` property as comma-delimited list (#790)
 - Fix type errors in PHP strict mode (#664)
 - Fix undefined local variable in `CalcFunction::parse()` (#593)
diff --git a/src/Value/Color.php b/src/Value/Color.php
index 85890393..07f11c34 100644
--- a/src/Value/Color.php
+++ b/src/Value/Color.php
@@ -225,7 +225,11 @@ public function __toString(): string
     public function render(OutputFormat $outputFormat): string
     {
         // Shorthand RGB color values
-        if ($outputFormat->getRGBHashNotation() && \implode('', \array_keys($this->aComponents)) === 'rgb') {
+        if (
+            $outputFormat->getRGBHashNotation()
+            && \implode('', \array_keys($this->aComponents)) === 'rgb'
+            && $this->allComponentsAreNumbers()
+        ) {
             $result = \sprintf(
                 '%02x%02x%02x',
                 $this->aComponents['r']->getSize(),
@@ -237,4 +241,19 @@ public function render(OutputFormat $outputFormat): string
         }
         return parent::render($outputFormat);
     }
+
+    /**
+     * Test whether all color components are absolute numbers (CSS type `number`), not percentages or anything else.
+     * If any component is not an instance of `Size`, the method will also return `false`.
+     */
+    private function allComponentsAreNumbers(): bool
+    {
+        foreach ($this->aComponents as $component) {
+            if (!$component instanceof Size || $component->getUnit() !== null) {
+                return false;
+            }
+        }
+
+        return true;
+    }
 }
diff --git a/tests/Unit/Value/ColorTest.php b/tests/Unit/Value/ColorTest.php
index 822ba5be..2b533a7f 100644
--- a/tests/Unit/Value/ColorTest.php
+++ b/tests/Unit/Value/ColorTest.php
@@ -54,6 +54,10 @@ public static function provideValidColorAndExpectedRendering(): array
                 'rgb(0, 118, 0)',
                 '#007600',
             ],
+            'legacy rgb with percentage components' => [
+                'rgb(0%, 60%, 0%)',
+                'rgb(0%,60%,0%)',
+            ],
             'legacy rgba with fractional alpha' => [
                 'rgba(0, 119, 0, 0.5)',
                 'rgba(0,119,0,.5)',
@@ -62,6 +66,14 @@ public static function provideValidColorAndExpectedRendering(): array
                 'rgba(0, 119, 0, 50%)',
                 'rgba(0,119,0,50%)',
             ],
+            'legacy rgba with percentage components and fractional alpha' => [
+                'rgba(0%, 60%, 0%, 0.5)',
+                'rgba(0%,60%,0%,.5)',
+            ],
+            'legacy rgba with percentage components and percentage alpha' => [
+                'rgba(0%, 60%, 0%, 50%)',
+                'rgba(0%,60%,0%,50%)',
+            ],
             'legacy rgb as rgba' => [
                 'rgba(0, 119, 0)',
                 '#070',
@@ -74,16 +86,73 @@ public static function provideValidColorAndExpectedRendering(): array
                 'rgb(0 119 0)',
                 '#070',
             ],
+            // The "legacy" syntax currently used for rendering does not allow a mixture of percentages and numbers.
+            /*
+            'modern rgb with percentage R' => [
+                'rgb(0% 119 0)',
+                'rgb(0% 119 0)',
+            ],
+            'modern rgb with percentage G' => [
+                'rgb(0 60% 0)',
+                'rgb(0 60% 0)',
+            ],
+            'modern rgb with percentage B' => [
+                'rgb(0 119 0%)',
+                'rgb(0 119 0%)',
+            ],
+            'modern rgb with percentage R&G' => [
+                'rgb(0% 60% 0)',
+                'rgb(0% 60% 0)',
+            ],
+            'modern rgb with percentage R&B' => [
+                'rgb(0% 119 0%)',
+                'rgb(0% 119 0%)',
+            ],
+            'modern rgb with percentage G&B' => [
+                'rgb(0 60% 0%)',
+                'rgb(0 60% 0%)',
+            ],
+            //*/
+            'modern rgb with percentage components' => [
+                'rgb(0% 60% 0%)',
+                'rgb(0%,60%,0%)',
+            ],
             /*
             'modern rgb with none' => [
                 'rgb(none 119 0)',
                 'rgb(none 119 0)',
             ],
             //*/
-            'modern rgba' => [
+            'modern rgba with fractional alpha' => [
                 'rgb(0 119 0 / 0.5)',
                 'rgba(0,119,0,.5)',
             ],
+            'modern rgba with percentage alpha' => [
+                'rgb(0 119 0 / 50%)',
+                'rgba(0,119,0,50%)',
+            ],
+            /*
+            'modern rgba with percentage R' => [
+                'rgb(0% 119 0 / 0.5)',
+                'rgba(0% 119 0/.5)',
+            ],
+            'modern rgba with percentage G' => [
+                'rgb(0 60% 0 / 0.5)',
+                'rgba(0 60% 0/.5)',
+            ],
+            'modern rgba with percentage B' => [
+                'rgb(0 119 0% / 0.5)',
+                'rgba(0 119 0%/.5)',
+            ],
+            //*/
+            'modern rgba with percentage RGB' => [
+                'rgb(0% 60% 0% / 0.5)',
+                'rgba(0%,60%,0%,.5)',
+            ],
+            'modern rgba with percentage components' => [
+                'rgb(0% 60% 0% / 50%)',
+                'rgba(0%,60%,0%,50%)',
+            ],
             /*
             'modern rgba with none as alpha' => [
                 'rgb(0 119 0 / none)',