There's a process in PI called B3E (Ballesteros Black Body Estimator) that can estimate missing data from a single colour filter if you have the other two. It is based on the assumption that the signal is generated by black body radiation. I've seen it do a fairly good job with missing a missing R/G/B filter and also creating simulated Ha from RGB data (not sure how accurate this is given that NB emission is not a black body process.)
A couple of PI forum threads about it:
http://pixinsight.com/forum/index.ph...28541#msg28541
http://pixinsight.com/forum/index.php?topic=9691.0
The paper that B3E is based on:
https://arxiv.org/pdf/1201.1809.pdf
Cheers,
Rick.