I've found two mistakes here, a too-short L shape at the top-center and a single pixel near the bottom-right corner. Luckily, their placement makes both an easy fix. Great job 

Really cool abstract tetris piece. Feels like an old mosaic tile artwork.

This is awesome! I've inspected the entry. 26 colours is a great result. Didn't found any forbidden shapes. None of the same colour pieces touches except the black. This is the only thing you need to fix, but you have more than 4 days for that. The whole black bar on the bottom, and also two black areas on the top right. This might help you. Overall fantastic work so far. Congratulations!