Custom suit and head editing (mostly) and making, where do I start?

[Pingonaut]

I've been working on editing some of the custom suits and custom heads, and I feel like I'm doing it very inefficiently. Here's how I do the suits:

I begin with the base texture.

By hand, I isolate the colored part of the suit (this part I feel like is the most inefficient, because with the red lining I can't seem to find the best place to cut it off as the colored part always affects the color of the red).

Then I edit as needed with Paint.net and GIMP. This is just not the process I feel it should be, and when it comes to custom Kerbal hair and eyes it's nearly impossible.

What's the actual best way to do this? Thanks.

Pingonaut