To begin please finish a lineart to whatever you're coloring. For this tutorial I'll be drawing and coloring myself. The lineart can be any color you wish. Personally, I like to use black or a slightly red-brown color to compliment the skin.
After making your lineart make two layers underneath it. On the furthest down you should use the fill tool to make a grey-brown color so you can see what you're doing. Next, select each piece of your lineart and color accordingly. Don't shade, that comes next (:
Now we add two darker shades to the skin. Do this on a layer above so that you can easily fix anything you have to. Next, copy and paste the layer with all the block coloring from step 2. Merge the shading of the skin down to the copied layer and blend.
Blend the coloring on the skin. Add the blush on the cheeks and nose (if you want)and blend into the layer. Erase any of the extra blush and shading over areas where it shouldn't be.Add any patterns or logos onto the clothes and partially shade lips. This has a lot to follow, bit it's a lot easier when you're doing it. (:
For this next part add two layers. Select your clothes, in this case the bikini. On the two layers change them from "normal" to "multiply". Shade on the first "multiply" layer witht he base color of the clothes. Next, go up to the highest of the two layers and do the same thing with the same color. It should be darker each time. After that finish the lips. Add in the color to the whites of the eyes - make sure it contrasts the color of the eye. Mine are actually hazel so I put purple to off-set that. Color in any piercings you might have and color any jewelry, also.
Blur the eye-whites with the water-brush tool. Drag the color down with white as your selected color. Next draw the white up. As in the diagram next to the picture, you'll finish that by going in small circles till you're happy with it. Next, move onto the eye lashes. Use the brush tool in SAI (if that's what you're using for drawing) and slowly shade with the deeper colors you want to use. Add a layer above your lineart and put the base color to your eyes.
Color the eye. To see how I did it look to the left of the picture. If you have any questions regarding the writing simply comment or message me. (:
Next, hide the layer where all of the coloring is. Make a new layer and put the base hair color on top of this. Then, shade with two darker colors and one lighter. If your person only has one hair color, skip the next few steps.
Add any other colors on layers above the shaded base. Change your eraser tool to "bristle" if you're in SAI and make it look like the base color is overlapping like normal hair would.
Erase around the extra coloring for the hair. Make the other layer of colors visible to make sure you didn't miss anything.
Finish off by adding contrast and saturation. Sign your name and boom, you're done! Hope you all enjoyed. Comment or message me with what I should do next (: