I know I managed to affect text in an SVG image by trying to make it a hyperlink in Harlowe - the text in the SVG essentially ended up being styled as a hyperlink, which looked terrible but seemed to open up a few intriguing options - so I'm hopeful that there's some way of doing it. But I probably would pick up a bit of SugarCube just to work with stuff like this. SVGs appealed to me initially just as a method of including images in the HTML without the unwieldy passages produced by Base64 URLs, but what you've done here shows just how much more they can do. (I've experimented with layered PNGs with transparent backgrounds as well - which might be easier under certain circumstances - but you'd need a truly absurd number of them to do anything like the kind of colour customisation you've got here.)
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.