these are my first attempts at making a shirt.
the left one is recolorable. The right one uses a stencil. I've read on the site, that they want you to make the designs recolorale...

But clearly either I'm doing it wrong, or this design is not made for this. First of all, I'm missing a color channel. I made it but I think the mesh doesn't support it.
Second of all, it looks crappy.

SO maybe I should make an in between? Make only the thick yellow letters recolorable, the rest not?

is that possible?

You can have a 4color shirt if you like but it depends if you are using CTU or TSRW.
I think the shirt original came with a 3 color option, not?(check the enabled patterns.)
In both CTU and TSRW you have the option to change it in a 4color design, last tab within CTU You do need to enable the extra pattern then and edit your mask texture with a extra channel(the alpha)

I say it depends wich one you use because i dont get it working in CTU, with TSRW i do

CTU doesn't load all the data for the fourth channel correctly, which can trip you up. If you're using CTU, you must remember to A) change Design Type in the Other Tab to 4 channel, and B) pick a pattern for channel D (even if you then switch it back to solid colour) and copy the Tiling over from one of the other channels.

It is harder to get clean lines using channels. You could perhaps use the overlay (or stencil) for the "separators", so that your channel edges don't have to be so clean.