I would change the graphics a bit, though - the "blinking" of the colour drops are a bit annoying when there are many. Also, the "doors" graphic has no real meaning (weather its up to down or left to right does not matter), so it could be changed to something block-like. The third improvement i would make is an indicator that tells that your "cursor" is "full" and does not pick up any more colours. Maybe you should differ the graphics of nonmixed and mixed colours - for example, you could "grey out" mixed colour drops while u are holding one colour in your cursor (for u cant pick up mixed colours, then), and "grey out" nonmixed colours while you are carrying around a mixed colour (for these cannot be picked up while holding a mixed colour) - this would make the game a bit more difficult, because the player would have to remember where which colour is while holding colours, if he doesnt want to pick up a specific colour on his way back (after opening a door and the colours becoming visible / "non grey" again). On the other hand it would ease up the thinking way a bit, the player wouldnt have to think "can I walk through these 6 colour drops with the colour i currently have without mixing it?" because the nonmixable colours would be grey during holding a colour.
Well, just my 2 centy, hope u understood what i meant xD (Not sure if i understand it myself any more xD)