Oh man, I rarely airbrush. I usually color in cel shading. And I actually prefer openCanvas to Photoshop... *SHOCK*. lol. My airbrush technique is basically just finding where the shadows would be and blending it in... LOL. I can give you a lot more advice on cel style (which you'll see in most of my drawings!)
Oh yup, I find it's easier for me to do airbrush coloring. Just keep on practicing it. I like Adobe Photoshop CS2 since I use that more often... *YEOWS*. Lol. I do the same thing by trying to find a color that is a bit darker than the first color & then use the Blur Tool to blend it in... LOL. I have never tried to color in any of my linearts with cel style (I'm quite impressed by ur other artworks!)
One thing that I do (a trick, call it) is lock the layers on the base color and then use the gradient tool to vary it slightly. (dark to light) Then, I duplicate the layer, erase it, change the layer type to subtraction or addition (might be called something else in photoshop, play around with it XD) and use that layer for shading. This way, the gradient is carried through and gives the picture more depth. If you look at my newer pictures more carefully, you will see that the whole thing looks like different gradients. Also, another thing I started doing was using SLIGHT airbrushing to make the results even more significant (like on my last 3 pictures. lol)
Alright then my friend (I'm listening, oh neat) I have never locked the layers for the base colors nor use the gradient tool to change it a bit (I use the gradient tool for skies & such). Oh like the copy & paste tools, erase it to suit the shade of ur colors, to alter it (It's the opacity tool in the layer tool box, then I shall play around with it ) and then use it for the shading. Thank you very much for the tips on how to give the artwork MORE depth. I shall have to check out ur newer pics to get ideas for my own pics. Okay then & thank you very much(I try to keep my digital pics simple. Lol.)!