Sounds like you are doing a clipping mask. Arrange your 2 objects (assuming both are vector objects) by positioning first the colored part how you want it, then put the paint daub above it. Select both objects, then go to Object >> Clipping Mask >> Make or Command-7 or CTRL-7.
If they are not both vector objects, use Photoshop to combine them.
Save early. Save often.
Jonathan Ziegler
http://www.electrictiger.com
520-360-8293