I hate throwing away paint - I have to use every last bit of it. Nowadays, I try not to ruin a painting by adding on more and more layers of watercolour (which is the best way to get mud, of course). Instead, I start another painting or experiment with it. Abstract exercises are the best excuse for me to use up gorgeous leftover colours.
Here is what I did with what was left of my poppy #1, following Rolina van Vliet's instructions. It would look quite nice as a large painting, don't you think?: