Color blind scheme

[eric-burel]

As there are multiple types of color-blindness we would need to figure a scheme that works for most people, or maybe different schemes.

In the survey form colors are defined via CSS variable so it's probably not too hard.

Not sure for the results app.

[SachaG]

Nivo supports patterns, this would probably be the best solution? cc @plouc

[shadow-identity]

As a note, I'm not color blind, but it's very hard for me to notice the difference on the right side. Maybe would be possible to add some extra contrast during the next iteration, to make default scheme more accessible for everyone (I don't think separate scheme for color blind people is a good solution).