Add a dedicated FromColor function, as I found using the ColorModel cumbersome.

oklab.go

@@ -106,6 +106,29 @@ func FromRGBA(r, g, b, a uint32) Color {
 	return FromNRGBA(r, g, b, a)
 }
 
+// FromColor converts an arbitrary color type to an OKLab [Color], with special handling
+// for [color.NRGBA], [color.NRGBA64], and anything implementing the [NRGBAColor] interface
+// to preserve transparent colors.
+func FromColor(c color.Color) Color {
+	switch c := c.(type) {
+	case Color:
+		return c
+
+	// Special handling for [color.NRGBA] and [color.NRGBA64]
+	case color.NRGBA:
+		return FromNRGBA(uint32(c.R)*0x101, uint32(c.G)*0x101, uint32(c.B)*0x101, uint32(c.A)*0x101)
+
+	case color.NRGBA64:
+		return FromNRGBA(uint32(c.R), uint32(c.G), uint32(c.B), uint32(c.A))
+
+	case NRGBAColor:
+		return FromNRGBA(c.NRGBA())
+
+	default:
+		return FromRGBA(c.RGBA())
+	}
+}
+
 func cube(v float64) float64 {
 	return v * v * v
 }
@@ -158,23 +181,7 @@ type NRGBAColor interface {
 }
 
 func okLabModel(c color.Color) color.Color {
-	switch c := c.(type) {
+	return FromColor(c)
-	case Color:
-		return c
-
-	// Special handling for color.NRGBA and color.NRGBA64
-	case color.NRGBA:
-		return FromNRGBA(uint32(c.R)*0x101, uint32(c.G)*0x101, uint32(c.B)*0x101, uint32(c.A)*0x101)
-
-	case color.NRGBA64:
-		return FromNRGBA(uint32(c.R), uint32(c.G), uint32(c.B), uint32(c.A))
-
-	case NRGBAColor:
-		return FromNRGBA(c.NRGBA())
-
-	default:
-		return FromRGBA(c.RGBA())
-	}
 }
 
 var (