Apparently our UI design decided to indicate that with red and green dots on the order line. If he had though about color blind users, normal users wouldn't have issues either.
That's what you meant, right?
Anyway, that's exactly the argument I always bring up: if you design for the colour blind, the deaf, don't assume righthandedness, etc, and you do it well, the interface will end up more user-friendly for everyone.
In your example, adding a hint based on shape/position/lightness (or all three even) as well as a colour is easier to read for everyone. Similarly, using some verion of Cubehelix[0] is the more readable option for heatmap-scales, and again not just for the colourblind but for everyone.
[0] http://www.ifweassume.com/2013/05/cubehelix-or-how-i-learned...
Yes, exactly.
More generally, any UX design that does not involve user testing (ideally with both new and experienced users) inevitably leads to the designers missing things. If there's one field where co-design is crucial to decent results, it's IxD.
https://en.wikipedia.org/wiki/Participatory_design