I’m not entirely sure why they call it red-green colour blindness, but the crux of it to me personally seems to mainly be a lack of sensitivity in the red part. For example, blue and purple often look identical to me, and it’s near impossible to tell the difference between shades of brown. If you put something green next to something red or brown they would often look the same and I wouldn’t be able to tell them apart. For example, when I look at this forum header, it took me several seconds, plus zooming my browser to tell the colour of the ‘latest’ box was red. Initially I wasn’t sure if it was red or green, but once I’ve seen it it’s clearer.
This probably sounds crazy to the 95% of people with normal colour vision, but for those who don’t it’s really stressful and for an application which forms such an important part of my workflow it’s really tough as it’s making me struggle to discern what it means and that just makes it more stressful than helpful!
For most people it’s not that we can’t see colours at all, but they are much less distinct. So, I can see the split circle for flagged/due but only when I really concentrate on it If I’m quickly scanning down the list in normal use the circles really just look ‘light grey’ or ‘darker’.
For what it’s worth, I’ve never really had this issue with any other software, but these particular colours on the light background are really problematic.
I’m fully aware that for most people this isn’t an issue at all and the colours used are fine, hence my only suggestion would be a simple flag for an alternate colour set. As an example, the video game ‘Call of Duty’ defaults to red/green markers to indicate opposing teams, but has an alternate colour set for CB players which changes to blue/yellow which solves the issue instantly.