Oh whew, I'll have to try that too! And ho boy...Base64. SVGs are a step up.
I've initially wanted to make a colour wheel of images, but that would have been too prohibitive if you wanted to give players a good selection. But just letting people pick whatever colour they want is such a step up.
I think I would only touch pngs again, if I had beautifully drawn art, but perhaps they could be combined together regardless. (Like SVGs only affecting solid colour spaces underneath the image) I think it might lead to some neat results.
With SVGs you kinda have to draw out every outline, so it becomes cumbersome if you have to work on multiple images and make sure every line connects. And sometimes some points get eaten up. (You can see in the game how some colours bleed over the border or don't reach the border at all) I'll get around to fixing that too.