Gem'X

The basic idea is that you are presented with 2 sets of tiles, and must make the left one identical to the 'control' set on the right. The colours are defined in a sequence - red, green, blue, purple, yellow - and when you click on a tile, that tile's colour moves forward by two in that sequence (for example a blue one becomes yellow), whereas the tiles next to it move by one colour (for example, blue becomes purple).