I have been trying to complete this level for some time.
I assume that, to clear a line, you need to change all colours vertically so that they are the same, which is why you get the colour paintbrush, then click and they should move the board to the left, bringing the block closer to the exit.
Sometime this works and the block shifts to the left as it should, sometime it doesn't.
Am I missing something?
Hope I have explained it ok.