How to optimally solve the flood fill puzzle?

Question

I like playing the puzzle game Flood-It, which can be played online at:

https://www.lemoda.net/javascript/flood-it/game.html

It\'s also available as an iGoog

Answer 1

A naive heuristic could be to use the number of colours left (minus 1) - this is admissible because it will take at least that many clicks to clear off the board.