You read my mind regarding frozen ones. Nasty surprise when I first encountered one thinking it was a skeleton only to find out was more like an uber-ghul. The light wraith-blue is perfect for both.

Frozen ones could be light blue, I agree. There are no other blue undead using "z" symbol and this color is lore-friendly (vel George Martin and his Others).
I'm not certain about ice statues and snow golems - we already have steel zombies which are encountered outside of dark forge and they are relatively dangerous monsters that ignore PV and have multiple attacks.
Instead, I'd advocate the usage of white and blue letter "I".
"I" already stands for some constructs, like humunculi or gargoyles so it would be fitting to use it for ice statues and snow golems.

There are enough blues to go around. Steel zombie blue isn't the same as icy wraith blue.

You have a point though, regarding gargoyles etc, they're essentially stone statues anyway, but imps, another I, are proper flesh and blood creatures I thought?

Gremlins, imps and quasits too, it seems.
No idea why are they actually represented by "I", other than the fact that "&" ran out of colors.
They belong to a group of minor demons after all, save maybe for gremlins.
Imps and quasits could be white or light blue "&".
Although the latter is already used for djinnis, those are arguably the rarest monsters seen walking around, they can literally only show up when a player uses a non-blessed RoDS, which doesn't happen too often.
Anyway, I think any single change right now would have a high chance of propagating and forcing more changes somewhere else and that's something I wouldn't want to see as a player.
I got used to stuff looking one way so it's ok to add new stuff, but not so ok to change existing things.

I have changed frozen ones tonight blue and ice statues, too. Hopefully people will occasionally look before attacking. The price of ASCII with limited colors :-(