I'm trying to texture paint a pattern onto a bowl but when I do, the original color of the transparency shows up behind the pattern. I had removed it, made the color transparent using Gimp. I would also like to know how to texture paint onto the original white material if possible. I want to keep the original specular and roughness.
You have to create and save two images, one with the alpha channel and the pattern and one that provides the white background for your bowl.
In your material editor, you're going to have the two images as image texture nodes, and the alpha channel all running through a mix node into the base color of your principled BDSF.
You can then open your image editor and open the background image of your pattern. You should also have a pane open in the "Texture Paint" workspace. If you don't have the right color, you can always paint bucket it white, or whatever is required.