Limb color does influence the final appearance of the skins. Black glass will darken the overall appearance, clear glass will lighten it. However, the difference is not great. The skins themselves can also vary quite a bit in color tone.
I would not paint the limbs. I have dyed the underside of the skins to darken them.
Be sure to roughen the surface with a flat sanding block before applying the skins. I use 120 grit sand paper. Some go as coarse as 80 grit. Of course, wet the skins and pat them with a paper towel or absorbent rag to remove most of the moisture before applying the glue. Either Titebond II or III will work.
When you put the skins on, you'll have about a half-hour to move them around to get them straight and work out air bubbles before the glue begins to set up. I give the glue one day to dry.
After trimming the edges, check to make sure the skins adhere along the entire length of the limbs. If not, you might need to work a little glue under any lifted areas with a toothpick.
Then do the masking tape to remove the scales. After couple applications of tape, view the limbs under a light, moving them around a little to identify any scales that still remain, and push them off with a fingernail/thumbnail.
I use Helmsman spar and it dries fairly quickly, if you spray it on thin, which you should. I generally do a coat every 6-8 hours, and usually apply 4-5 thin coats. Be sure to hit the skin/limb edges on every coat you apply.
Beginning to end -- about 3-4 days. God luck.