Most of them don't have any
added color, just the actual color of the flavoring compounds themselves. Sometimes you'll see some added color here and there, like if you find a liquid that's colored blue or green, for example. But when it's just varying different shades of yellow or brown, that's just the natural shade of the flavor compound(s).
Unflavored liquid is either crystal-clear, or very very slightly yellow if it's a high enough nic strength. I can see a yellowish tint in the 60mg base I use for DIY, but once I cut it down to the 3 or 6mg that I actually vape, I don't see any color left at all. Straight-up menthol is pretty clean, too. If I'm just vaping unflavored, or only menthol, then my wicks and coils will last for months. Any flavored liquids, though, even if they
look completely clear, will still leave that gunky black buildup within a few days, if that's what you're concerned about.