The little indoor (admittedly not normally used) is quite deep.
The warm up and test arena are both rubber (and yes will stain white legs) but when I was there last month I don’t recall it being too deep. Maybe a touch in the walk ways between the 2 test arenas?
I’ve not done dressage there but have jumped. I personally don’t really like the indoor (for jumping this is the warm up) but I like the outdoor. Found indoor a bit deep.