Installed Hell Gate London, the Legacy mods (SP1.2 and MP2.0) - starting up the game after each install. I then installed mod un3.0 using the Revival 1.5b launcher, and the Essence icons are blank. So far, everything else seems to be working fine - and when I hover the mouse over the grey square it identifies the Necro and Beast Essences - just no colorful green and red circles.
Strangely enough, on an earlier install, I first loaded mod 1.5b2, and then loaded un3.0. In that case, the Essences had color graphic icons.
Addendum: So I compared the 2 dat directories, and there were 2 files missing from the 2nd install: sp_hellgate...4580.dat and 4580.idx. I copied them over, and the Essence icons appear as they should.