ALL amps 'color' the sounds, but I've played quite a few of those 260s and they aren't at all like you are saying.
I find them mellow, old school and although they are in no way a giant killer, they can hold their own against many practice amps. The operative here is 'practice amps'.
I own almost everything Acoustic makes by now except that 260, a B-200H and anything of theirs in a Neo version.
I just don't see a need to practice on one amp and play out on another - that's not my style.
Neos to me sound too bright - but it might just be the smaller cabs where the sound just doesn't come out as I would like it to.
I'd take the 260 back and trade up to a B-450 and prepare to hear a very good amp at a low price and obviously one with that old school thump and boom tone.
If you turn ON the horn in the 450, it will break glass - so you can use that to temper your sound even more toward a modern, glassy tone - not MY idea of a good bass sound, but you may like it anyway.
BTW: What strings are you using?