I don't think that most people are getting them to match their switch colors since most people seem to be ordering one of each. I think there's really two ways to look at it:
1. Use black and red only. The two red keys would serve the same purpose, such as both being control, and the two black keys would serve the same purpose, such as both being alt.
2. Use four different colors. You'd then probably do a running suit of cards on the right alt, meta, right super and right control keys.
I think I like the second way a bit more, which is more for looks than for function. You could do the second way with just black and red too, but I think the different colors would be more eye catching. Regarding the color for the club, brown is good to match the switch color but if we aren't going for the switch color match then I think that green is better. Green is the color used in four color decks of cards (as pictured above). Green is a also just a nicer color than brown and the club is also sometimes referred to as a shamrock/clover so it suits it well in that regard too.