Silver and gray are shade colors, which means that basically any color will go well with it. Just pick whichever color(s) you like the most.
I have a white/black/gold bike, and will be doing a combination of white/orange/red, partly to keep relatively legal to keep cops off my ***, and cause it matches the bike the best. My bike used to be yellow and black, and I did a combo of blue/green.
Safety being number one, anything that increases visibility is a good thing. Perhaps you don't want to use red or blue, lest police give you a hard time for stealing their colors. No personal experience but it seems to be the consensus that this is a real issue many places.
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