Actually I managed to make a mistake in doing my server fix which caused all the UIs to crash in Single Player. I just fixed that and re-re-enabled the staff moss UI. It seems to work on both client and server.It doesn't work. It looks like the code to register it isn't there. I tried adding it but the game crashed every time I tried to trigger the UI. I assume that the feature wasn't finished. Vipix hasn't touched the mod (at least on GitHub) for two years so I think it's safe to say that it won't be finished.
If you mainly just want to change the colour of grass you could try using regular grass and painting it using the palette, which does work quite nicely.
LyraelRayne/VipixToolBox fixed version here.