Character editing is hard until you learn exactly how most things work In game. Like any sort of coding/scripting, it requires a lot of knowledge on how the engine works and how things are handled in game. It took me about a year of using Ono before I was actually any good at it, and about 2-2/12 years to get to the point where I know pretty much exactly how to make things work the way I want them to.
The good thing is once you’re proficient at it, it becomes like second nature and is really just time consuming at that point. If you want to learn faster I suggest heading to the Gameplay modding thread here
Making custom colors shouldn’t be too hard; however, making full blown custom costumes is very hard and time consuming and requires a lot of knowledge on 3D modeling and rigging.