What's the best colour for a 4WD?

Colour, colour, colour.  From a purely practical perspectice white is all right, because it is the coolest, in the literal sense of the word - white reflects heat.  White also doesn't show scratches as easily as darker colours, it goes with pretty much every accessory colour and resale won't be affected.  White also doesn't show the dust or dirt very much.  That's why all mining and uitity 4WDs are white.

Now if we leave aside pure practicality there's a host of other options:

Silver - means you were trying to be trendy and upmarket in 2005-2010. But in 2011 and onwards white has become the trendy colour of choice, but only gloss-finishes, not the utilitarian whites of working 4WDs.  One has to be different, one supposes.

Black - attempts to convey an air of sinister suaveness but doesn't work because the car is permanently dirty and the owner sweats inside

And as for the other colours, if they're all pastel shades that's just boring, but if they're bright enough to stand out:

Green - must be lover of old British racing cars

Red - passionate, different, sparky

Pink - like red, but also desperate for attention

Blue - traditionalist, would love a red car but doesn't dare

Brown - wanted to be different but missed the mark and scored a bullseyse for boring.  No car has ever looked good in brown paint. 

Grey - lacking imagination, or something, can't quite think what

Yellow - fun & cool

Orange - rare, like the drivers, and that's a good thing!