This is where the family came in. Last Sunday I had all three of my kids throwing paint around making "textures" for the Spartans strip. Some of these I would drop in as backgrounds, adjusting the colour to suit, and others I would make a transparent layer of and lay on top to texture the colours.
Here's how it works:
I start with a spread, speedily inked in Manga Studio. Notice the lack of colour...
Then get my children to make an unholy mess with paint. Here comes the colour...
here are the final pieces drying
I scan those in and then paste them all over the spread, which by now has a few flat colours added. The result is something like this.