Trough dichromatic eyes/seeing no or less colours
Uhm, I read once a text written by a person in the rare position of not being able to see colours, and she said that instead, she was more able to see patterns and how they fit together, in clothes for example. (It was a womans magazine.)
If you go for just not being able to see red, which would result in them seeing brown, green and red - and hues with those colours in it - as the same colour, which could result in them being less able to use colour coded maps or warning signs etc. but also in getting less distracted by bright colours and wounds and such, simply because to them, those are no different in colour then, say, a tree.