They're reasonable looking, however, I would say to you to follow the shading off the greyscale (i.e. where the grey goes a shade lighter, you choose a colour which is one shade lighter of what you are painting over it with, because it will make the planes look more 3d. Also remember that you have to fill out the entire spritesheet for each aircraft (a sprite is one of the little planes with the blue surround, a spritesheet, which we also might sometimes call just sprites is a file with the 40 or so sprites which need painting for going into the GRF). Other than that use the ottd palette, because if you use other colours they will not work in game, also there are some colours on the spritesheet you shouldnt use, for more info on that go here:
http://dev.openttdcoop.org/projects/worldairlineset/wiki/PaletteOther than that, these are great paints and we are really happy to have someone new aboard. Add me to MSN if you have it (if my email is not on here, search for me on tt-forums.net under the same name). Alex.