Background color/wallpaper is considered a non-feature as there is no obviously clean way of implementing it without causing conflicts with other applications relying on wlr layer shell protocol. Instead of reimplementing parts of swaybg in srwm, you can just use swaybg (or most other wayland-compatible wallpaper applications) in the autostart section of the configuration. My stance on this may change in the future.
[autostart]
once = swaybg -c 00ff00
# or
# always = pkill -x swaybg; swaybg -c ff0000
The short answer is no, and it probably never will. You may be able to get the window groups feature to replicate it.