Andy and all...

Here's a possible inexpensive hardware approach to detecting when an aircraft is in clouds or not... "Balloon-borne disposable radiometer for cloud detection"

https://aip.scitation.org/doi/10.1063/1.3685252

It is used on Radiosonde balloon soundings to detects being in cloud. I handed the information over to one the stewards at the 2012 WGC Uvalde. The paper and detailed design is mostly behind a pay wall. This idea could be used to add information onto an IGC recorder. Not easy... trying to implement this into our gliding competition systems. But, it has the potential advantage to giving a measured metric for identifying when gliders are in clouds.

Walter Rogers WX