Minor I've tried what you said about angeltekno project, but still appear the same colors for the blocks.
There are 18 different frames, and the 19th is for the "special" block. I used choose (1, 1, 2, 2, 3, 3, .......) and nothing happened. I even used (1,1,1,1,1,1,1,1,1,1, 2, 3....) but all the blocks appeared with the same frequency. I think the problem is the formula for setting the animation frame which is: (Block.Color-1)*3+1, but if I change it, the game doesn´t work properly.
Moreover, right now the special block doesn´t match with any other special block.
Any idea of what the problem is?