Thanks for the reply.
I believe on your blog, you also have an interview with Tamura Sensei? He talks about using kiko/chi gung excercises to "look inside" his body.
Would you know, if Ueshiba Sensei referred to these colours, did he ever use an unusual kanji, for example 覧る, when talking about seeing them?
I don't recall seeing it offhand, but I'll keep my eyes open!