moved gradient test location

d2compiler/compile_test.go

@@ -3894,20 +3894,6 @@ svc_1.t2 -> b: do with B
 				tassert.Equal(t, "d2/testdata/d2compiler/TestCompile/meow.d2", g.Layers[0].Layers[0].AST.Range.Path)
 			},
 		},
-		{
-			name: "test-gradient-fill-values-in-sketch-mode",
-			text: `
-				vars: {
-					d2-config: {
-						sketch: true
-					}
-				}
-				x->y
-				x.style.fill: "linear-gradient(#000000, #ffffff)"
-				y.style.fill: "linear-gradient(#ffffff, #000000)"
-			`,
-			expErr: "",
-		},
 	}
 
 	for _, tc := range testCases {

d2renderers/d2sketch/sketch_test.go

@@ -1357,6 +1357,14 @@ item -> customer: is(Adult)
 customer -> item: true
 `,
 		},
+		{
+			name: "test-gradient-fill-values-in-sketch-mode",
+			script: `
+				x->y
+				x.style.fill: "linear-gradient(#000000,#ffffff)"
+				y.style.fill: "linear-gradient(#ffffff,#000000)"
+			`,
+		},
 	}
 	runa(t, tcs)
 }

lib/color/color.go

@@ -86,6 +86,8 @@ func darkenCSS(colorString string) (string, error) {
 }
 
 func LuminanceCategory(colorString string) (string, error) {
+	// check if colorString matches the `url('#grad-<sha1-hash>')` format
+	// which is used to refer to a <linearGradient> or <radialGradient> element.
 	if IsURLGradientID(colorString) {
 		return "normal", nil
 	}