Start a new document of 400x400 and using the Bucket Tool paint the background white. Select the Horizontal Type Tool and write a sentence or any word using your favorite color.
Step-2:
Click on Layer-Rasterize-Layer and go to the layers pallete and check the LOCK box.
Step-3:
Grab an appropriate Paint Brush and change the color you want to paint your font with. I used assorted yellow. Start brushing the areas you want to change colors to.
Step-4:
And this is the end result. I hope you enjoyed this tutorial.