[scientaster]

It's not equivalent to what OP made, the logic is slightly different. It took 5 minutes and it was just to demonstrate how easy it would be to make something similar. If you wanted to mirror OP you could build out the pixel struct to have a color to value mapping.

The penny auction one is even easier:

  bytes3[10000][10000] board;
  function colorPixel(uint x, uint y, bytes3 color) onBoard(x, y) { 
    board[x][y] = color;
  }

Users would only have to pay the gas cost of using the ethereum network, the contract wouldn't hold any funds itself. Again, it's pretty much whatever you make out of it. You're not really constrained when it comes to building in logic into these contracts, anything (logically) you can do with any other languages is possible here.