I've always just called those "twigs". Also, I've not forgotten your request about the arches; I'm working on getting something together for you.
Regarding hues, drop me an ICQ.
EDIT:
While I keep working on a more complete rubble index, here's a temporary answer regarding arches. Counting both orientations, there's 6 types (unless I'm forgetting one offhand):
The pictures don't line up properly here; imagine each of the pieces aligning along the top (instead of the bottom, as here). For the middle 2 arches, half-height walls can also be used to 'widen' them without looking out of place.