Does a comouter interface with preamp color the aound?
 

I'm looking at the focus rite Scarlett. My question is, since this has a preamp in it, would It color the sound the way an onboard pre would?

Not really, at least not if it's competently designed. A bass pre is supposed to colour the sound to some degree. A general purpose pre amp such ass the FocusRite Scarlet is supposed to do that as little as possible (and that isn't a difficult task.)