Pretty good looking...
Could be a few things but most likely I would have thought is it's getting screwed up when reducing the colour depth to 8bit.
Do the colours match on the textures your working on? Does it still look screwed up if you use a different method to reduce the colour depth?
If thats a Spit14 and your using an alpha mask to get rid of the annoying blue bar under the cockpit. I had this exact same thing start to happen to me on the Typh skin I did. Not sure exactly why it started doing it on me but there's one or two things you can do to try and fix.
Make sure you alpha mask is 256 colour greyscale.
If the are under the blue bar is solid colour you can dump the alpha mask and just fill in the area and it shoud look just fine.
Gatso