Add an alpha property to a Css.Color grassland -- "{ value = "#56bf74", color = Compatible, red = 86, green = 191, blue = 116, alpha = 1, warnings = [] } : Css.Color" withAlpha 0.5 grassland -- "{ value = "rgba(86, 191, 116, 0.5)", color = Compatible, warnings = [], red = 86, green = 191, blue = 116, alpha = 0.5 } : Css.Color"