The sketch was originally drawn in black by tablet via photoshop, but I adjusted the outline’s colors once the drawing was finished. This can be done by doing the following. While on the base layer (which is your drawing) go to (Image–>Adjustments–>Color balance) and adjust the color to your liking! 🙂
Always create a new layer for each element in your drawing. For example, create a layer for skin, hair, details etc. If it helps any, label your layers skin, hair etc. Go to (Layer>New>Layer) and create a new layer. Change the layer mode to Multiply so you don't have to worry about interrupting your pencil drawing below. I almost always start coloring the skin first. No idea why but that's how I've always done it. I colored this just as I would color anything else. I then applied the burn tool and used the curve feature (Image>Adjustments>Curves)
For the hair, I chose a bright, neon pink and applied similar techniques as I did with the skin (Burn tool> midtones and highlights). Hue and Saturation as well as color balance came in handy for this part too. I wanted to make this as bright and cheerful as possible.
Added a little color and shading to the ears. Plus I colored in the eyes on this layer as well. I don't normally do this but I was feeling a little lazy :p.
Added glare to the irises and a little on the hair and skin as well. I try not to over do the glare. You can use the dodge tool for this but what I did was I created a new layer and kept the layer mode as 'Normal'. Then you paint the areas of the hair, face etc. that you want glare to be in. Once you're done with that, go to Filters>Blur and select Gaussian blur. Adjust the radius to about 7.2 to create a blur effect on the glare spots.
The finished product should look something like this!