From Robinson's own SN-25, Issued Dec 1986, Updated July 2012:
Pressure drops and fuel evaporation inside the carburetor cause significant cooling. Therefore, carburetor ice can occur at OATs as high as 30°C (86°F).
@bvgs:
I was hover taxing the other day at just under 25 inches of manifold pressure (almost at full weight) and the gauge was going well into the minus. No big deal ….
As the yellow arc is -20 degC to +5 degC or so (from memory), it seems you were operating well beyond normal operating conditions and sudden engine failure initially masked by governor operation was a distinct possibility. Some might disagree with you and call that quite a big deal.