I had noticed when I went to paint my 3D models I had nowhere to put the paint. Rather than go out and buy one for $10-$15 I just decided to try my hand at designing one myself using fusion 360. I think it came out pretty good for the amount of time I spent on it. Let me know if there are any improvements I should make, and if you have any questions.
This specific model's diameter is just around 4.7 inches due to the fact I never need much paint at a time and thought the smaller size would make it more portable. Obviously you can scale up or down to fit your needs accordingly.
(I am going to gloss my print over with a spray on clear coat to make cleaning it easier, but it's not necessary.)
I am planning on printing and uploading photos of my results later this week.
Pantone Cool Grey
UPDATE: I rounded out the sides of the "dip" to make for a cleaner look and add for space for the paint.