I solved these issues abandoning tradional icons (BMP,PNG) to SVG. I started too from Google Material Design SVG icons but with a different approach because I needed icons not present in these libraries (some I drew, others I took from other online free libraries). So now I've several SVG sprites (some Google MD some customized) all designed 24x24 with black as the main color and I pick images from these sprites (for buttons, imagelists etc). SVG are pure XML so it's not difficult to change on the fly size or color (you have just to change an xml attribute or xml node), so, when I need SVG for dark theme or I need to use the sysop accent color I just change black stuff in the desired color. For me now is easy to reach something like this:
I started these "revolution" on my apps about 4 years ago to approach both HIDPI monitors and dark mode and it was quite a lot of work; in that period SVG it wasn't as fashionable as now so I had to build some internal components myself to do this job. Now it seems that there are even opensource solutions that help to solve these problems.
SVG is scalabale and is a text file. I don't like EMB approach of virtual image lists in which you have to provide several rastered icons for different sizes: Material desing base icons are 24x24 so if my app is 100% zoomed it uses this size, if the zoom is 150% ii switches to 36x36, if the zoom is 357% it uses 85x85 and so on, so the SVG images are rendered always of correct size for every zoom applied.
I've categorized all my SVGs and each of them has a name like "confirm", "cancel", "exit", "print" etc. I've inerithed the components in which I need SVG stuff (buttons, images, ecc) adding a property in which I provide at design time just the SVG name and then all is solved at runtime as the program needs (style, size, zoom etc). In this way if I want to change/update an image I just modify the SVG sprite.