[R] Query for semi-transparency support

[Jesse Brown]

In ?par there is the following line:

 "Semi-transparent colors are available for use on devices that support them."

I'm looking for a way to query for that support on the current device.
I'm pretty sure that this functionality exists at some level as I
remember seeing warnings to this effect but my searches have come up
empty. Is anyone familiar with a direct path to this information?

Thank you,

Jesse