I'm sorry but the colors in red 1 and 5 are practically indistinguishable, at least on my monitor. That has turned the puzzle into a torment instead of a fun :(
People kept telling me the same thing mars2mercury recommends, but they never said how. Go to Settings (that gear icon), then choose Advanced Settings. Scroll to the bottom, the option you need is the third from the bottom, IIRC.