In my personal opinion, you have to choose whether you want the rider or the mount to be the focus on your model. While a large enough model can have multiple points of focus, from a distance your color choices and paint scheme will draw the eyes to one point first.
For me, the model is about the Lord, and not the dragon. Knowing that the LC's armor was the light, airy-esque blue gold I'd started I wanted the dragon to fit into that scheme while also being a darker color. This way the super bright highlights on the help of the LC would be the main focal point. At the same time, the dragon couldn't be too dark, nor too contrasting a color, otherwise it would draw attention for the opposite reason as above.
Step 1: Basing Black and Washing Burgundy
Knowing I wanted the model to be darker than the LC, I went back and painted over all the skin area with black. I then mixed a custom wash of red / blue / purple to create a deep burgundy color. It look rather intense in this picture, and it also is still wet so it looks glossy. But the main effect here is what I wanted - The darkest parts of the dragon will be this color, wash with some Nuln Oil, and my layers will be thinned down enough to show this color through.
Note on skin and base colors: Lots of people don't know this, but the reason that some painters can achieve super realistic skin and flesh tones is because of the undercoat. By applying red, blue, yellow, or green to the model, you can drastically change the look and feel of the creatures skin. For healthy, 'good' characters some form of red or pink is a great choice. For dead characters blue works great, and for rotting characters green works well. Doing this gives the skin a feeling of 'depth' which you can't achieve in a single layer. Anyways...
After the red based dried I began picking out the transitions. The more transitions (i.e. colors) you can get on a model such as a dragon, the more 'realistic' and beautiful the model becomes. This is achieved through washes, layers, and dry brushing.
I played around with colors in the palate I am using, and decided I wanted the beast to go from the red base, to a brown I'm using the leather of the models, to a 50/50 brown teal, to a teal which goes with the armor well. Using very thin paint and lots of reducer helps make sure that your paints don't dry too quickly but also don't become washes. We want the tops highlighted in the scales, not the recesses, so either don't thin you paint so much it runs, just enough so that it would take two or more coats to cover well - this way the base coat is showing through.
After working through the colors, from bottom to top, I have the model at a stopping point. I also went through and repainted the horns, cloth, and other areas that were over-sprayed with my original base grey color.
I also did some work on the base at this point, BEFORE FINAL HIGHLIGHTS, as the angle of the model is slightly different than it is intended out of the box. I also will need to add the rider before final highlights are done, as all these things influence the strength and location of those highlights. I will cut the foot off the supplied base / rock thing it comes on, and paint the base separately (again without final highlights), then put it all back together.
I'll cover the base creation technique in a separate post.
The whole model will now get a wash with Nuln Oil to give it some black linking, which will have a big impact on the areas where the armor meets the cloth and scales. Now to let the base dry a bit before I cut the dragon off and proceed.
I hope you enjoyed this WIP, please leave questions and criticisms in the comments section, always looking to help and improve.