Hi there,
After a little research, I finally found a way for editing skins color only, without affect the original design.
Thanks to Zdzichu, who opened this thread, and thanks to Way and AntraX, who gave him the solution, I decided to edit the color of Kleer Kurt skin.
I wanted to change its color into Modican bovine mantle, that is considered as a 'red' mantle.
After a conversion with TexConverter, and using color curves from Paint.net, I made it.
I converted the skin thumbnail, too. But it looks more red than the skin itself.
And this is a thumbnail copy more green and less red:
But I decided to also keep the original Kurt, so this new one will be additional.
I obtain two results: the first one was too red; so, for the second one I decreased the red and increased the green a bit. But I still think I'm far from perfection. In the screenshot below, you can see a graphical glitch when spawning or respawning.
That's why this is stll an alpha skin.
This is how it looks under the light. It seems a bit darker than the bovine mantle, but my objective is to reach its color.
I reduced the resolution, because of my connection that doesn't allow me to upload over 1MB images.
PS: the modican bovine race is from Modica, in Sicily. But, in Sardinia, we have them, too. It was about 19th century, some people brought a number of modican bulls here and hybrized them with sardinian cows. But there are not so many differences between modican and modican-sardinian hybrid, although they are considered 2 different races. Also, this race has some changeability in the mantle color (some black in some cows, and some other ones who don't have it).