This repros for me. However while testing this out I noticed that works on most most colors except for:
Black (0, 0, 0)
White (255, 255, 255)
Red (255, 0, 0)
Green (0, 255, 0)
Blue (0, 0, 255)
Yellow (255, 255, 0)
Cyan (0, 255, 255)
Magenta (255, 0, 255)
It seems that if all the sliders are set to 0 or 255 then the rounding error or whatever is causing this problem doesn't seem to take place.