This is where the magic starts. How do you color those grayscale pieces you ask me! It's kind of tedious work actually, you have to be careful, and it takes a lot of practise to actually become any good at it!
Some people use layer functions like multiply and whatnot, but I don't like that.
I use a series of commands, three mostly, but sometimes four. Those commands are ;
command + M = Curves
command + U = Saturation*
command + B = Color Balance*
IMAGE - adjustments - variations
The main TOOL I use, is the lasso! The symbol in the toolbar loks just like a lasso. The key to getting this to work for us, is the settings. Fuzzyness. Variations in fuzzyness is extremely important, and somethign to keep an eye on in each step you make for coloring!
PART 1.
There are different things to keep in mind depending on HOW you are going to color your drawing! So, decide that FIRST! I decide I'm going to turn Sir Buckton into a Seal Bay, which is a very dark bay with lighter golden/orange tender areas.
BEFORE I start coloring, I need to lighten the areas that will be lighter than the rest. this is becuase if you try to lighten after you color, you will get horrible looking gradients! If you try, you'll see what I mean.
So, we have our lasso tool. We want the fyzzyness to have a big spread (Think of fuzzyness as a blur filter around the edges of something) to avoid harsh transitions. So, we for the largest areas, elbow and hip, I pick 50% fuzzyness. For the jaw I pick 20. For the muzzle area I pick 15. The reason why you don't see the dashed selection around the muzzle is becuase soemtimes a warning window will appear that say something about the selection beeing too small to be shown. This is all right, just click ok, the selection is still there.
Now that we have our selection, we start with command+M, and get a dialog box like in picture 2. Use it to lighten. Keep the selection active - we don't want to exagerate with the curves in command+M, so after that we go tu command+U, and get a window as in picture 3. Lighten again.
Invert the selection with command+shift+i. Use command+M to open the curves window again, and darken. There, now we have sifficient contrast in the base.