The 757s are for the most part ETOPS rated equipment if I'm not mistaken and they are routinely flown back to the states for service on CO trunk routes, and even include CO's smaller routes to Europe flown with the 757.
Eventually there may be a dedicated fleet of 757s just for Air Mike, but right now it fluctuates. Air Mike does have DC-10-10 and DC-10-30, along with 727-200s complete in its lettering, you'll probably see the 737-800s recieve this as well.
(I wonder how the folks on the Island Hopper route are going to think about the 737-800 (BG)...it's a source of talk on Guam and Saipan from what I hear.)
I expect more of a definition of fleet painting once their 767-200/400 and 777-200 fleet are completely online and the phaseout of older equipment is finished, then you'll see a more established brand name on their fleet. Until then, you'll see the gaps in identity even though they are essentially all the same. (G)