Painting!!! I love the game of Warhammer... I love the hobby fifty times more. Now, I have a blog with awesome battle reports AND paint. High Five!!!
Ok... Now to the thoughts on your wonderful toy... I'm going to offer up lots of ideas which I would consider for this radical centerpiece. That said, they are still only ideas and opinions, so take them however you'd like!
For the tongue, I'd go with a purplish-pink. It'll keep a nice warmth with your scales and should look natural. Ask yourself, what color is this dragon's meat? Think of a giant dragon flank steak and come up a notch or two.
I like your brown idea for the wings. That surface is huge and will draw a lot of attention to a stunningly contrasted dragon beneath. Go for it!
Your red is solid. If anything, I'd consider adding one more top highlight to it. Perhaps take a fiery orange and add a > touch < of bleached bone (or similar) to brighten it and hit the top edges. It will add some serious pop, contrast with the dark scales, and tie in to your plan for tooth, claw, and horn. You can shade the scales - some of the larger ones, anyways - with well-watered-down dark green. The complimentary color will also add some striking visual interest for when you get really close.
The black skin is going to be a chore. I really like the feel here, and it works wonderfully from a complete composition angle, but I've painted a lot of black and even they need depth. The tricky part with black is giving it contrast without making it grey/blue/purple/green etc. I'd suggest the following:
- medium thin highlight of shadow/space wolves grey. Keep it a bit watered down, but you'll want to line the ridges, ripples, and bumps. This will give you a good base for...
- thin toplight with ghost grey. This is your fierce contrast color here. When I think of black beasties, particularly scaled ones, I imagine some serious gloss. This sharp highlight will help you achieve that look.
- Finally, take an ink/wash (GW's are awesome), I'd suggest purple, mix in a tiny bit of black paint and a tiny bit of your red paint (I'd say a final mix of 1:1:5:10 of black:red:wash:water) and glaze the entire thing, using your brush to pull excess off of your toplight. This should give you a decent blend on the non-blended highlights used as well as give your black some color interest. You can also use this glaze for the brown wings. It'd be a nice way to tie the whole package together, too.
Again, just my 2 cents. I know you'll do a fantastic job and I can't wait to see it!