Well like many posters did say, Abe didn't need Big Face after he got his hand scars. I'm sure Big Face is off training other newbies.
I think his blue skin is probably just a random genetic occurance, like an albino Slig
By the way, did you notice that in the intro to AO's Rupture Farms, there were blueish mudokons pulling levers? (unless the lighting was blue or something)