Luminance with color red doesn't work well

[debu66er]

bb8.color("red",-0.5); shows light red color but bb8.color("red",0); and bb8.color("red",0.5); show exactly the same red color.

0.5 is not brighter than 0 as I understood it should be from the examples. I tested to change between them several times and there is no change. I just see change with -0.5