Welcome.
In terms of colour choice, it is very much a matter of personal preference. The vast majority of these cars appear to be blade silver or gunmetal grey so anything out of Black, Azure (blue) or Sunset (rusty) is often popular. Some of these colours had slightly different tones and names for facelift editions, but these are very close.
Much more rare are: white, chilli red, yellow (was this only for GT4 cars originally?).
Even more rare than all the above is a cool metallic purple colour which wasn't offered in the UK.
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At the end of the day it depends on what you like