Image texture is not applied on the hairs when I reopen Blender (2.8) I'm trying to texturize the hairs of the 3D character using the projection painting tecnique. At the beginning the hairs are separated objects from the body. Then I spread the texture taken from a picture over their surface and finally I attach them to the rest of the body and I save the file.

But,when I reopen Blender (2.8),the base color is applied,but not the image that I want. I tried to join the objects in two ways. Before I have selected the hairs and then the body and I have joined them,but it didn't work. Then I tried to select before the body and then the hairs and I have joined them,but also in this case the image texture is not applied when I reopen the file. What's the solution here ? You can see what I did going here.
If you make sure your UV map is clean enough to paint, then you can paint and then save the image to disk so it will keep the changed pixels. Using the image texture through an image texture node, you can specify the uv map to use so that it stays put in case you have multiple uv maps for other materials in your object.