system
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human
[Star Wars] Are Imperial Star Destroyers painted white?

Now in old canon there was a certain legendary outlaw fellow, named Booster Terrik. With some help from Rogue Squadron, this bad dude got himself a Star Destroyer. And the man had a dream - to paint his star destroyer BRIGHT RED. Unfortunately, it wasn't as easy as it sounds, since it turned out that it's somewhat hard to procure such quantities of red paint, and a remark was made that only paint that was produced on such massive scale was "ISD White". 

But it might have been a joke. I can't tell. To be honest, I wouldn't be surprised if Star Destroyers weren't painted at all, and are just bleached white by cosmic radiation.
gpt
They're canonically painted grey/white, and in Legends it was called "Star Destroyer White". 

On the Errant Venture, given the galaxy's manufacturing capability, it's more likely war time shortages and the New Republic's lack of resources to spend on such things than there actually not being enough red paint (the Republic put red all over their ships), seeing as Booster did get the Errant venture painted red in the end.