Well, Roger, I'm afraid I'll only muddy the waters with this bit of info...
First, "Das Heer Maria Theresias", the facsimile of the Albertina-Handschrift, confirms the general details of the troopers' uniforms, but not those of the trumpeters, except to note that they wore the tricorne and coat, as we already knew.
I checked in my copy of Osprey's "The Austrian Army 1740-80: 1 Cavalry". In a note informing us that "some gaudily colored coats are recorded", the authors note specifically that Kalnocky's trumpeters wore a light yellow coat with silver lace. The SYW Project's (Kronoskaf's) article cites Knoetel for its info on the musicians, and list the color as scarlet with blue cuffs and silver lace and edging.
I don't know for sure, from these two different descriptions, but I suspect that either one could be correct, but may have been used at different times. Red/scarlet and yellow/gold were the colors used on the Saebeltasche, and it makes me wonder if those were the colors of Count Kalnocky's livery.
Do you have 2 of those figures? You could paint both variations then ;D
Prost!
Brad