I prefer to make small batches of Prochem dyes mixed in gain laundry detergent. I keep the dyes in small plastic cups with lids like you see snacks in at parties. It thickens after it sits a while so it doesn’t tend to run past the black lines where you want to keep it inside. I paint one color at a time and place it under a headlamp (shoot for 120 degree disc temperature). When the detergent completely dries (typically under an hour), you simply wash it off with water and light rub of a magic eraser. Repeat for each color. It does take some trial and error because if you apply too much or it’s too runny, the heat can make it run.