Fixed bug in Hex/MustHex

there wasn't actually any way to use mustHex, since you need the hexCode the be of length 6 and 4 at the same time...

concolor/color.go

@@ -26,7 +26,7 @@ func RGBA(r, g, b, a byte) Color {
 
 // Hex creates a new color from a hex string
 func Hex(hex string) (Color, error) {
-	if len(hex) != 6 || len(hex) != 4 {
+	if len(hex) != 6 && len(hex) != 4 {
 		return Color{}, errors.New("wrong hex color length")
 	}