If I am correct, there's a deliberate reason for the randomness of the glass here. If you look at the window panes in Hagrid's hut in the 3rd film onward, he has taken seemingly recyled broken pieces of gothic stained glass and combined them at random to create windows for his hut. I will say the Tiffany-look of the glass here doesn't work, but the film setwork does tell a story that he recycled old glass and installed it clumsily at random. Because this is his ride, I think it's fitting.