What is the best way to color a model? I have made a model I'm happy with and want to color it. I have used UV mapping for this but now I have learned maybe that wasn't the best thing to do...

Only one object in the model shows up in color at a time, but when I see other peoples models they are fully colored. 

I'm just really confused, I don't know what I did wrong. Are all the objects like hair, eyes, clothing and skin meant to be all attached on one layer? I assumed not because I'm going to be rigging it later. 

If anyone could give me some advice or point out what I'm doing wrong it would be extremely helpful as I'm just struggling a lot and don't know anything about 3d modelling. 

I heard that there is this thing called texturing but I don't know if that's different to UV mapping. 

I just want colors on my character. What is the best way to do this?
One thing you can do is texture painting. That allows you to add different colors to your model and apply all of that color to the material of the object. Here's a good tutorial: https://www.youtube.com/watch?v=LcCQKuWPhXk