SickofNexus

I'm extremely new to modding in any capacity and I wanted to make a custom skin colour for Skyrim. Trouble is, I don't know how. So my question is how do you edit a skin texture to change its colour and make it it's own setting in game? I do have Photoshop and the texture files, I just don't know how to open and edit them in the way I want. If anyone could give me a step by step run down that would be grand.

Is there a simple retexture mod that can change the color of the horse at Whiterun stables to be more black and less brown? I have no way of doing this myself but it's just something that really bugs me especially since I like collecting all of the horses.