The Steps1. Make sure whatever patterns you're going to be usin inside the brushes are already defined as a pattern!
Create a new layer and put your brush cluster down in whatever color you want.
2. Hold in the CTRL key on your keyboard and click the little thumbnail preview of brush layer, which I outlined below in red.
3. Click on the brush tool. Click on the basic circle brush that should have came with your photoshop. Make it a small size (mines 10px but it depends on your brush that you're filling.
Color in the inside with a random color like this
4. Once you're finished coloring it in, click on the colored ins thumbnail preview. It should be selected now.
6. Click "Layer >> New Fill Layer >> Pattern >> ok >> Choose your pattern. Click ok. Drag the pattern layer under the brushes layer.