You want a 0 (zero) back space.
I'm not writing to contradict Paul here but do check this out first...
IIRC the standard 5-spoke Colorado alloys are not zero offset... If you look on the rim, there are some numbers cast into it; the first set will denote size & fit (say 16 x 7JJ) & then there is another number denoting offset... You might find a -15 on the rim which equates to -15mm offset
The only reason I know this is from when I changed my wheels on the Colorado from standard alloys to 80 series alloys - the 80 series alloys are certainly zero offset which is what I wanted to fatten up the stance... But its been a while since I did the swap
Hope this assists - have a look & see what you find
PS: I have 275/75/16 BFG AT tyres on the Colorado & there's a wee bit of rubbing with the offset wheels on hard lock - nothing disaterous though. I personally think its quite a good size for the 90.