Here is an assignment for my image manipulation class (photoshop class).. The assignment was to just color an original drawing.. Im currently animating a similar thing like this so i figured it was a good idea to colorize a frame.. Ive included some steps to colorizing pictures in photoshop.. Im by no means an expert at this but this is what i know to this point..
Step 1.. this is a scanned drawing of the picture.. you want to go to your levels and play with the color output to darken all the lines.. then you want to duplicate this layer.. The top layer is line art and the bottom is your color layer. Never color on you line art layer or you lines will get all fucked up.. (unless you want colorized lines).. Also your line art layer needs to be set to Multiply mode and your color layer to normal mode..
step 2.. In this step you want to duplicate your line art and put this on a layer below.. this is you color layer.. I then go to levels and turn make the white space inside the turtle into about a 20-30% grey.. then i paint on top of this..sort of an underpainting.. once youve done this lock your transparent pixels..
step 3..Its important to lock your transparent pixels on your color layer so you dont color outside your figure
step 4... The big turtle is done, his skin is composed of about 3 shades of green.. dark, mid, and a really whited out version of green. His chest plate is only two shades of a tan color.
step 5... I color in the shell and then add a texture to it in filters (texturizer) Im not sure you can see the texture in the final picture.
step 6 .. all i need now is a background