I've got a dent in a tail rotor on a 222 from landing in a confined area on a clear day at -40C and idling for twenty minutes waiting to load our patient. When we lifted out of the hole, I was suprised to see all the fog that had formed around us (I couldn't see it while in the hole), flying out the machine gave quite a shudder and on landing we had a nice ding in the tail from shedding ice.
At 9000 feet at -29 C in a S76 we picked up so much ice the pitot heats couldn't keep up. Watch out for the tops, they are the worse.
So I've picked it up from the surface to 9000 feet, from 0 C to -40 C, and pretty much everywhere in between. I'd recommend avoiding cloud below zero, or at the very least, seriously limiting your exposure, as I've been caught a few times.