Apply theme colors to SVGs OR trigger alternates based on light/dark background

Hello! I've been developing a flexible set of themes and templates that can be set to match various color combinations from my company's branding.

One of the features is that when a user goes to "background styles" on the design ribbon and selects a light or dark color, key elements of the design switch from light to dark or vice versa, while others remain the same. 

The challenge I'm having is that in my version of Storyline (v3.66.28355.0, controlled by my company) I'm unable to set the color on SVGs, so I can't set my custom branding shapes to a color that will update when the theme flips.

Is there any way to set an image (either vector or raster) to change appearance based on the background color? If I can't assign one of the colors that automatically changes, is there perhaps a way to set up alternate states of an image, then add code or triggers to make that change? It wouldn't be visible in build mode, but I was thinking perhaps when the timeline started on a slide, these graphics could automatically change state to contrast the current background color. I haven't been able to find any variable that I could use for such a thing, but it seems like there must be something.

If you know of any way to make graphics change color based on background style or color, please let me know!