I just realised that my NERDTree directory colour wasn’t inline with my Vim theme, and I couldn’t help but be bugged by it. Seems it’s a simple change. To change colour you need to use the treeDir highlight group.
:hi treeDir guifg=#96CBFE guibg=#00ff00
To keep it synced with the ir_black theme I use, I just added the following to my colour scheme file.
hi link treeDir Keyword