Nav Bar Icons not changing to gray on apps with light theme

Question

I have used adb to add working volume buttons to the nav bar on my Fire tablet (Pie version of Fire OS), but I'm running into a few problems:

• The volume icons I used (Google Fonts Icons) do not automatically change to gray (like the stock back,home,recent buttons do) in apps that change the nav bar to white/light theme. See pictures: Volume buttons on black/dark theme Volume buttons on white/light theme

• In landscape mode, the back,home,recent buttons are now extremely spaced out. Adding more spaces in the adb code to squeeze them closer together ends up making them too close together in portrait mode. See picture: Buttons in landscape mode

Wondering if there is a way to fix these problems using adb, or changing something in the command I used. This is what I used:

settings put secure sysui_nav_bar "space,space,key(25:file:/storage/emulated/0/volumedownwhite.png),space,back;home;recent,space,key(24:file:/storage/emulated/0/volumedownwhite.png),space,menu_ime"