I love the juxtaposition of hot and cold color. The effects you accomplish in your sky are breathtaking. I know you do your coloring digitally now, did you use a particular brush or technique to achieve that twinkling yet cloudy sky effect? It's so reminiscent of watercolor...
I made a bunch of custom crunchy brushes in Photoshop, and then used them to make the cloud/nebula sky.
I open up a new document, and then with my FG/BG colors set to Default (black and white) I use the Cloud filter. The document is filled with clouds!
I then Threshold the image, making all the couds 'Bitmapped'; they are either black or they are white. No grays!
Using the Lasso tool, I make a sloppy selection around any nice black cloud shapes, and then do Define Brush. I save the shape as a brush. I made about 30-40 cloud brushes this way!
Then, in any illustration, I can use the cloud-shape brushes to make clouds. Setting the opacity of the brush to 15% or so, I just go around making cloud shapes. I will cycle throughthe brushes using the < and > keys, and you'd be surprised how many great clouds you can make. If you want a really solid cloud, just click over and over in the same spot. If you want wispy edges, just click a few times.