Thanks Tim, those look great.
Following on from Iain's advice I think I'm going to go with the grey coat/red facings look though. In fact, here's a cheeky wee proof of concept fellow I've recently completed:
As for flags, the red cross on yellow background for the Regimental flag is exactly what I'd imagined, especially as the Burke/Bourke coat of arms looks a bit like this:
I'd probably include the lion on the Regimental flag too.
For the Colonel's colour I think a plain yellow field with the red cross pattee and possibly the motto "Ung roy, ung foy, ung loy".