I literally stumbled onto the contest last week. But I love the idea.
So here is what I was able to come up with in about a week:
[edit: wrong url]
http://www.java4k.com/index.php?action=games&method=view&gid=321
Got enough bytes spare to add deselecting on a second click?
Actually, a friend of mine brought that up too. I think I can slip it in under the 4k. I’ll refresh it tonight. Thanks for the input!
Screw waiting for tonight, I modified it now. It now will deselect if you click on the same box twice. Hope you enjoy.
Last change, I swear. I removed a kind of crappy effect when secondary colors where deleted and added an “undo” button. So you can back up just one move.
Definitely helps. Thanks.
If you’ve got a few more bytes and a bit more time… A level transition would be good - even if it’s just displaying the completed board and then going to the next level on a mouse click. (If you can fit in a “Next” button that would be even better).
And unless the instructions are meant to be cryptic and force us to figure things out, it would be convenient to list the primary colours and go into a lot more detail on rule 2. Otherwise I have to choose between just playing more-or-less at random or taking notes myself as I go along.
I don’t want to come across as just a nit-picker, by the way. What you’ve done is pretty good for a week, and I understand that polish in 4k is hard. But the extra challenge of squeezing in as much polish as you can means extra pride in the achievement. 
No, no! I appreciate the feedback. And honestly, I have no real aspiration to win this. I mean there are a couple of 3D rendered entries and even the other block puzzle is pretty amazing. But I do think this is a great learning opportunity so the feedback is gold to me.
I’ve been thinking of dropping the tutorial button and having the first 3 levels automatically be the tutorial. And then maybe I can squeeze in a transition. I’ll see what I can do, and post to this thread when its up.
Thank you, again.
Okay, changes are up. The tutorial is now automatically the first 3 maps and there is a transition.