My guess would be that if the SI lists the Yellow buoy as the mark for the monohull fleet, you should round that one regardless of where it sits.

If, however the SIs refer to "outer course" and "inner course", you'd probably have to round the further buoy regardless of color/shape.

Unless, of course, the RC is flying the appropriate flag to indicate course/buoy changes.

What was the PRO's response to your inquiry (assuming you or someone else inquired)?