Here's a general breakdown for the Wolverine illustration:
1) Sketch Stage: I use to sketch in pencil and then scan but these days I do everything in photoshop, including the linework. What you're not seeing here, is I start of with a rough drawing of the line of action or motion of the body, then loose volumetric shapes to fill in the mass. Afterward, I sketch the actual drawing itself, which is what you see here.
2) Render Stage: I always paint in greyscale, this insures the values of an illustration read clearly. You can't rely on colour alone to distinguish things. One of my teachers always insisted one must ensure a drawing communicates well in black and white, adding colour is just the icing on the cake. A quick way to work is also to just duplicate layers or parts of a painting in order to adjust values. I don't usually just go right into painting heavy darks. Usually, it's a pretty flat under-painting, the same values of shadows all across just as a base. Then I duplicate layers, mask it out and paint away to reveal what's already there, and that's how I start to build up the darker areas. I'll touch up areas with paint afterward to blend things better.
3) Colour Stage: Once the rendering is done, colouring is very quick at this point. I just block out the colours and adjust the opacity level. I usually have the read as a 'color' layer in photoshop, 'overlay' and 'soft light' are used sparingly.
4) Final Stage: At this point, I'm tweaking and balancing colours, shadows and highlights. I always add a global colour at the end, meaning I add one colour over the entire character (usually 5-10% opacity on a 'color' layer). I do the same thing to the background, and then one more over the entire illustration. This harmonizes all the colours, theirs nothing more distracting than competing colours, saturation and contrast levels. This particular painting is fairly rough, you can tell the difference between this and some of my more detailed concept paintings because I'm using few brushstrokes, broader and looser. Something like this, takes a lot less time. This one took maybe 4 hours I'm guessing.