This is a very minor detail, but I realised that when I enabled Grudge's UI mod, the white icon borders and the big, fat, yellow selection border, which I both wanted to remove as they would block my building icon's effect symbols, would reappear. This is because he assigned the factions new UI groups, which were not being overridden by my mod. So, I went ahead and created new folders, under the headings of his new UI culture groups, and replaced them with something which, I think, complements his mod.
When you have both my and Grudge's UI mod installed, you will get colour-coded selection boxes which represent which culture you're playing as. For example, if you're playing as Rome, you will have a red selection box (Latin - Red). If you're playing as a Greek faction, you will have a light blue selection box (Hellenistic - Light Blue) etc. If you don't have Grudge's UI mod installed, then you just get the default, yellow selection boxes for every faction.
Also, on an extra note, I have gone through the building culture group tables and updated each building's icon to now be unique rather than share icons. Previously, when I changed the Roman faction's icons, there were some factions who had their icons changed as well (e.g. Barbarian ports, Greek religious etc shared Rome's icons). Now, provided that I create the icons, each faction's buildings will now have unique icons with their own effect symbols. This was really tedious, but it had to be done.
DEFAULT
(Grudge's UI mod not installed / culture group not assigned)
GRECO-ROMAN
HELLENIC
BARBARIAN - CELTIC
BARBARIAN - GERMANIC
NOMADIC
EASTERN
EGYPTIAN