diff --git a/test.cpp b/test.cpp
index 25fa852..3b1ddfc 100644
--- a/test.cpp
+++ b/test.cpp
@@ -37,20 +37,60 @@ void ASSERT_EQUAL(const optional<Color>& expected, const optional<Color>& actual
 
 int main() {
     try {
-        ASSERT_EQUAL(Color{ 255, 128, 12, 0.5 }, " rgba (255, 128, 12, 0.5)");
+        ASSERT_EQUAL(Color{ 255, 128, 12, 1 }, " rgb (255, 128, 12)");
+        ASSERT_EQUAL(Color{ 255, 128, 12, 1 }, "rgb(255,128,12)");
+        ASSERT_EQUAL(Color{ 255, 128, 12, 1 }, "RGB(255,128,12)");
+        ASSERT_EQUAL(Color{ 255, 128, 12, 1 }, "rgb( 255 , 128 , 12 )");
+        ASSERT_EQUAL(Color{ 255, 127, 0, 1 }, "rgb(100%, 50%, 0%)");
+        ASSERT_EQUAL(Color{ 255, 127, 0, 0.5 }, "rgb(100%, 50%, 0%, 50%)");
+        ASSERT_EQUAL(Color{ 255, 128, 12, 0.5 }, "rgba(255, 128, 12, 0.5)");
+        ASSERT_EQUAL(Color{ 255, 128, 12, 0.5 }, "RGBa(255, 128, 12, 0.5)");
+        ASSERT_EQUAL(Color{ 255, 128, 12, 0.5 }, "rgba(255, 128, 12, 50%)");
         ASSERT_EQUAL(Color{ 255, 255, 255, 1 }, "#fff");
+        ASSERT_EQUAL(Color{ 255, 255, 255, 1 }, "#FFF");
+        ASSERT_EQUAL(Color{ 255, 255, 255, 1 }, "#fFf");
         ASSERT_EQUAL(Color{ 255, 0, 17, 1 }, "#ff0011");
-        ASSERT_EQUAL(Color{ 106, 90, 205, 1 }, "slateblue");
-        ASSERT_EQUAL({}, "blah");
-        ASSERT_EQUAL({}, "ffffff");
+        ASSERT_EQUAL(Color{ 255, 255, 255, 1 }, "#ffff"); // NOTE: level 4
+        ASSERT_EQUAL(Color{ 255, 255, 255, 0 }, "#fff0"); // NOTE: level 4
+        ASSERT_EQUAL(Color{ 255, 0, 17, 1 }, "#ff0011ff"); // NOTE: level 4
+        ASSERT_EQUAL(Color{ 255, 0, 17, 0 }, "#ff001100"); // NOTE: level 4
+        ASSERT_EQUAL(Color{ 255, 128, 12, 1 }, "rgb(255 128 12)"); // NOTE: level 4
+        ASSERT_EQUAL(Color{ 255, 128, 12, 0.5 }, "rgb(255, 128, 12, 0.5)"); // NOTE: level 4
+        ASSERT_EQUAL(Color{ 255, 128, 12, 0.5 }, "rgb(255 128 12 / 0.5)"); // NOTE: level 4
+        ASSERT_EQUAL(Color{ 255, 128, 12, 0.5 }, "rgba(255 128 12 / 0.5)"); // NOTE: level 4
+        ASSERT_EQUAL({}, "rgb(255 128 12 0.5)"); // NOTE: slash is required before alpha
+        ASSERT_EQUAL(Color{ 255, 127, 0, 1 }, "rgb(100% 50% 0%)"); // NOTE: level 4
+        ASSERT_EQUAL(Color{ 255, 127, 0, 0.5 }, "rgb(100% 50% 0% / 50%)"); // NOTE: level 4
+        ASSERT_EQUAL({}, "rgb(100% 50% 0% 50%)"); // NOTE: slash is required before alpha
+        ASSERT_EQUAL(Color{ 0, 0, 255, 1 }, "blue");
+        ASSERT_EQUAL(Color{ 0, 0, 255, 1 }, "Blue");
+        ASSERT_EQUAL(Color{ 0, 0, 255, 1 }, "BLUE");
+        ASSERT_EQUAL(Color{ 112, 128, 144, 1 }, "slategray");
+        ASSERT_EQUAL(Color{ 112, 128, 144, 1 }, "slategrey");
+        ASSERT_EQUAL(Color{ 112, 128, 144, 1 }, "SlateGrey");
+        ASSERT_EQUAL({}, "slate-grey");
+        ASSERT_EQUAL(Color{ 0, 0, 0, 0 }, "transparent"); // NOTE: transparent black
+        ASSERT_EQUAL({}, "blah"); // NOTE: invalid color name
+        ASSERT_EQUAL({}, "#fffff"); // NOTE: invalid hex code, five digits
+        ASSERT_EQUAL({}, "ffffff"); // NOTE: invalid hex code, no hash prefix
         ASSERT_EQUAL(Color{ 226, 233, 233, 0.5 }, "hsla(900, 15%, 90%, 0.5)");
-        ASSERT_EQUAL({}, "hsla(900, 15%, 90%)");
+        ASSERT_EQUAL(Color{ 226, 233, 233, 0.5 }, "hsla(900, 15%, 90%, 50%)");
+        ASSERT_EQUAL({}, "hsla(900, 15%, 90%)"); // NOTE: missing alpha value
         ASSERT_EQUAL(Color{ 226, 233, 233, 1 }, "hsl(900, 15%, 90%)");
-        ASSERT_EQUAL(Color{ 226, 233, 233, 1 }, "hsl(900, 0.15, 90%)"); // NOTE: not spec compliamt.
+        ASSERT_EQUAL(Color{ 226, 233, 233, 1 }, "hsl(900, 0.15, 90%)"); // NOTE: not spec compliant
         ASSERT_EQUAL(Color{ 0, 0, 0, 1 }, "hsl(9999999999999999999, 0, 0)"); // NOTE: float precision loss
         ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(45, 100%, 50%)");
         ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(-315, 100%, 50%)");
         ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(-675, 100%, 50%)");
+        ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(45, 100%, 50%)"); // NOTE: degree unit is implied
+        ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(45deg, 100%, 50%)");
+        ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(45DEG, 100%, 50%)");
+        ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(405deg, 100%, 50%)");
+        ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(-315deg, 100%, 50%)");
+        ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(-675deg, 100%, 50%)");
+        ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(0.785398rad, 100%, 50%)"); // NOTE: pi/4
+        ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(0.125turn, 100%, 50%)");
+        ASSERT_EQUAL(Color{ 255, 191, 0, 1 }, "hsl(50grad, 100%, 50%)");
 
         // Out of range:
         ASSERT_EQUAL({}, "xxx");