Got an excellent and very exhaustive reply by the master of all things Colonial and purveyor of the finest miniatures, Col Mike Snook.
For those interested in most cases the colour mentioned as 'facings' is actually the trim around the 'bib'/ Officers and some Nco's replaced this with gold or silver. Rarely the inside of the bib was of a different colour than the uniform (Alkaluk or kurta) Not all that much different between these two. from what I can see the alkaluk opens all the way down to the front while the kurta doesn't open all the way. (Put on like a blouse)
Below one of those rare instances where the bib is in the facing colour (pink) From the Iron Duke website