[TOMT] [Book]Older children’s chapter book

This book is for children’s age of perhaps 8-13. I used to read it all the time as a kid, but I was an advanced reader so I’m not quite sure of the appropriate audience for the book.

The book was a short chapter book. I used to read it roughly between 2002-2009.

The cover was yellow with a hand and it was holding a paintbrush with paint.

The book is about a boy who loves to paint. He hears about opal mining in Australia and sets off on his own to look for opals.

The main thing I remember is that he needs money so an owner of a store hires him to paint his storefront. He goes around asking people in the Australian desert in their mobile homes (I think?) for leftover paint. He has a bunch of small amounts of many colors so he paints the store many different colors.