The problem with onion toppings on pizza is that they’re too slimy. I used to like them on pizza but you have to weigh the good with the bad. Try lots of bell pepper instead.
Wait until the pizza is done, then apply the mandolin sliced paper thin onions. Not slimy or stringy. Better flavor. I also only add my Asiago, or Romano cheese to the pizza once it is done and out of the oven. Try that. All the old world difference.
Red, orange or yellow are the best bet. Use green if you don't like your dinner guest or are incredibly cheep.