Making TF2 workshop items paintable using GIMP

This guide assumes you generally already know what you're doing and already have a model and a texture ready to be uploaded to the TF2 workshop. It explains how to make workshop items paintable using GIMP as opposed to Photoshop.

Introduction

This guide assumes you have already made a hat/cosmetic for TF2 and a texture for said hat.
There are guides which explain making hats paintable using Photoshop, but the guides for doing this with GIMP are all outdated.
So, here's how it works.

Step 1: Selecting the areas to be paintable

TF2 uses whatever is whiter or "lighter" in the alpha channel to determine what parts of a cosmetic are paintable.
Also, you'll usually want to have whatever part of your texture you want to be paintable in a white color, usually a creamy white color (the default, non-painted version of the creamy white colored part of your texture can be set to any color you want in the beta importer later on, so don't worry if you wanted the paintable part to not be a white color by default). The paints will automatically be applied onto this color.
Here's an example of a texture I made. The white strips on the left side are what I want to be paintable, so I will select them using the Fuzzy Select tool and then pressing SHIFT+CTRL and then do a Colors Select (within the fuzzy selection) to select the white stripes.

Step 2: The alpha channel

Now that you have selected the areas to be paintable, don't select anything else from here on out. Keep the area selected.
Now, we're going to add a layer mask to our texture. Do this by right clicking your layer and clicking "Add Layer Mask" (if you don't see this option or it's grayed out, add an Alpha Channel first to your layer).
Select "Black (full transparency)"
After you do this, your texture should disappear (this is a good thing, don't worry!) but your selection should remain visible.
Now, you're going to want to fill your selection with pure white (FFFFFF).
And that's it! Export your texture like you normally would (TGA 512x512 scale, also be sure to uncheck RLE compression)

Step 3: The beta importer

The rest should be straightforwards. Just import your paintable texture and model into TF2's Beta Importer, check paint VMT, and set the RGB team color values to whatever you want (should be a red one and a blue one, of course, but it doesn't have to be) and when you preview your item, you should be able to apply paint to it! Now you don't have to spend a million dollars on Photoshop, yay!
*In this example, I ended up making the mushrooms paintable instead - but it's the same exact process.

[GRUNK]

i share luciamo's problem

[tracer cheater wayfer chaser]

Does this also work with paint.net?

[Luciamo]

Nevermind I fixed it, thank you for the guide.

[Luciamo]

Hey, I'm having an issue where at the end of the guide when I port it over, the alpha blacks out every other part of the texture. Do you have any tips, or know where I might of messed up?

[Elena ღ]

Great guide it really helped me JO