It can be difficult to find some really good tutorials in CG colouring. Although experimenting is the best with different software, it's good to know some of the ins and outs in using them. Can give you some advice on colouring with Photoshop, though it depends sometimes on what version you have available, in order to make use of some features, as more streamlined basic versions won't have the addons in others. It also depends on what type of colouring you intend to do using software like Photoshop.
To do that its good to have an idea of how the layering techniqies in Photoshop work. Examples in a detailed tutorial are best to work with. Elfwood for example has an extensive range of online tutorials for various art media, and this one is exceptionally good at giving some pointers on using Photoshop to colour a pencil-shaded drawing, using layering techniques, paint brushes, and shading.
It might help point you in the right direction.
Tutorial on colouring pencil drawings in Photoshop
