Thanks so much!
The water color paper texture was done with a couple of textures and parameters in the vector art software I use, Inkscape. It's an overlay that I mask to each tile. To be perfectly honest, I don't remember the exact parameters I used, since I tend to just copy the one I already made 😅
But I could probably make an "empty" tile with just the texture and a light parchment color add it into the next set.