diff --git a/internal/css_parser/css_decls_color.go b/internal/css_parser/css_decls_color.go
index 4944a8679f0..240b2a61998 100644
--- a/internal/css_parser/css_decls_color.go
+++ b/internal/css_parser/css_decls_color.go
@@ -300,13 +300,13 @@ func (p *parser) lowerAndMinifyColor(token css_ast.Token, wouldClamp *bool) css_
 		}
 
 	case css_lexer.TIdent:
-		if text == "rebeccapurple" && p.options.unsupportedCSSFeatures.Has(compat.RebeccaPurple) {
+		if p.options.unsupportedCSSFeatures.Has(compat.RebeccaPurple) && strings.EqualFold(text, "rebeccapurple") {
 			token.Kind = css_lexer.THash
 			token.Text = "663399"
 		}
 
 	case css_lexer.TFunction:
-		switch text {
+		switch strings.ToLower(text) {
 		case "rgb", "rgba", "hsl", "hsla":
 			if p.options.unsupportedCSSFeatures.Has(compat.Modern_RGB_HSL) {
 				args := *token.Children
@@ -379,15 +379,15 @@ func (p *parser) lowerAndMinifyColor(token css_ast.Token, wouldClamp *bool) css_
 				}
 
 				if removeAlpha {
-					if text == "rgba" {
+					if strings.EqualFold(text, "rgba") {
 						token.Text = "rgb"
-					} else if text == "hsla" {
+					} else if strings.EqualFold(text, "hsla") {
 						token.Text = "hsl"
 					}
 				} else if addAlpha {
-					if text == "rgb" {
+					if strings.EqualFold(text, "rgb") {
 						token.Text = "rgba"
-					} else if text == "hsl" {
+					} else if strings.EqualFold(text, "hsl") {
 						token.Text = "hsla"
 					}
 				}
@@ -463,7 +463,7 @@ func parseColor(token css_ast.Token) (parsedColor, bool) {
 		}
 
 	case css_lexer.TFunction:
-		switch text {
+		switch strings.ToLower(text) {
 		case "rgb", "rgba":
 			args := *token.Children
 			var r, g, b, a css_ast.Token
@@ -591,7 +591,7 @@ func parseColor(token css_ast.Token) (parsedColor, bool) {
 					if v1, ok := args[2].NumberOrFractionForPercentage(); ok {
 						if v2, ok := args[3].NumberOrFractionForPercentage(); ok {
 							if a, ok := parseAlphaByte(alpha); ok {
-								switch colorSpace.Text {
+								switch strings.ToLower(colorSpace.Text) {
 								case "a98-rgb":
 									r, g, b := lin_a98rgb(v0, v1, v2)
 									x, y, z := lin_a98rgb_to_xyz(r, g, b)
diff --git a/internal/css_parser/css_parser_test.go b/internal/css_parser/css_parser_test.go
index b3afbe4831c..c0da178b7f9 100644
--- a/internal/css_parser/css_parser_test.go
+++ b/internal/css_parser/css_parser_test.go
@@ -556,6 +556,11 @@ func TestColorFunction(t *testing.T) {
 	expectPrintedLowerMangle(t, "a { before: 0; box-shadow: 1px color(display-p3 1 0 0 / 0.5); after: 1 }",
 		"a {\n  before: 0;\n  box-shadow: 1px rgba(255, 15, 14, .5);\n  box-shadow: 1px color(display-p3 1 0 0 / .5);\n  after: 1;\n}\n", "")
 
+	// Check case sensitivity
+	expectPrintedLower(t, "a { color: color(srgb 0.87 0.98 0.807) }", "a {\n  color: #deface;\n}\n", "")
+	expectPrintedLower(t, "A { Color: Color(Srgb 0.87 0.98 0.807) }", "A {\n  Color: #deface;\n}\n", "")
+	expectPrintedLower(t, "A { COLOR: COLOR(SRGB 0.87 0.98 0.807) }", "A {\n  COLOR: #deface;\n}\n", "")
+
 	// Check in-range colors in various color spaces
 	expectPrintedLower(t, "a { color: color(a98-rgb 0.9 0.98 0.81) }", "a {\n  color: #deface;\n}\n", "")
 	expectPrintedLower(t, "a { color: color(a98-rgb 90% 98% 81%) }", "a {\n  color: #deface;\n}\n", "")
@@ -640,6 +645,7 @@ func TestColorHSLA(t *testing.T) {
 
 func TestLowerColor(t *testing.T) {
 	expectPrintedLower(t, "a { color: rebeccapurple }", "a {\n  color: #663399;\n}\n", "")
+	expectPrintedLower(t, "a { color: ReBeCcApUrPlE }", "a {\n  color: #663399;\n}\n", "")
 
 	expectPrintedLower(t, "a { color: #0123 }", "a {\n  color: rgba(0, 17, 34, .2);\n}\n", "")
 	expectPrintedLower(t, "a { color: #1230 }", "a {\n  color: rgba(17, 34, 51, 0);\n}\n", "")
@@ -660,9 +666,13 @@ func TestLowerColor(t *testing.T) {
 	expectPrintedLower(t, "a { color: hsla(-200grad 2% 3%) }", "a {\n  color: hsl(-180, 2%, 3%);\n}\n", "")
 
 	expectPrintedLower(t, "a { color: rgb(1 2 3 / 4) }", "a {\n  color: rgba(1, 2, 3, 4);\n}\n", "")
+	expectPrintedLower(t, "a { color: RGB(1 2 3 / 4) }", "a {\n  color: rgba(1, 2, 3, 4);\n}\n", "")
 	expectPrintedLower(t, "a { color: rgba(1% 2% 3% / 4%) }", "a {\n  color: rgba(1%, 2%, 3%, 0.04);\n}\n", "")
+	expectPrintedLower(t, "a { color: RGBA(1% 2% 3% / 4%) }", "a {\n  color: RGBA(1%, 2%, 3%, 0.04);\n}\n", "")
 	expectPrintedLower(t, "a { color: hsl(1 2% 3% / 4) }", "a {\n  color: hsla(1, 2%, 3%, 4);\n}\n", "")
+	expectPrintedLower(t, "a { color: HSL(1 2% 3% / 4) }", "a {\n  color: hsla(1, 2%, 3%, 4);\n}\n", "")
 	expectPrintedLower(t, "a { color: hsla(1 2% 3% / 4%) }", "a {\n  color: hsla(1, 2%, 3%, 0.04);\n}\n", "")
+	expectPrintedLower(t, "a { color: HSLA(1 2% 3% / 4%) }", "a {\n  color: HSLA(1, 2%, 3%, 0.04);\n}\n", "")
 
 	expectPrintedLower(t, "a { color: rgb(1, 2, 3, 4) }", "a {\n  color: rgba(1, 2, 3, 4);\n}\n", "")
 	expectPrintedLower(t, "a { color: rgba(1%, 2%, 3%, 4%) }", "a {\n  color: rgba(1%, 2%, 3%, 0.04);\n}\n", "")
@@ -673,6 +683,7 @@ func TestLowerColor(t *testing.T) {
 	expectPrintedLower(t, "a { color: hsl(1deg, 2%, 3%, 0.4%) }", "a {\n  color: hsla(1, 2%, 3%, 0.004);\n}\n", "")
 
 	expectPrintedLower(t, "a { color: hwb(90deg 20% 40%) }", "a {\n  color: #669933;\n}\n", "")
+	expectPrintedLower(t, "a { color: HWB(90deg 20% 40%) }", "a {\n  color: #669933;\n}\n", "")
 	expectPrintedLower(t, "a { color: hwb(90deg 20% 40% / 0.2) }", "a {\n  color: rgba(102, 153, 51, .2);\n}\n", "")
 	expectPrintedLower(t, "a { color: hwb(1deg 40% 80%) }", "a {\n  color: #555555;\n}\n", "")
 	expectPrintedLower(t, "a { color: hwb(1deg 9000% 50%) }", "a {\n  color: #aaaaaa;\n}\n", "")