Gotcha. Thank you for this info. Yeah, your pair looks like our 10-pack, lighter brown on dark brown. Never seen the yellow-and-black one. If not too much to ask, could you please post some pics from Google images search to show in pictures the difference you are mentioning in words? I wonder what exactly you saw, even if just examples, not the exact fish of your peers that you saw.
Also, it looks like I erroneously thought it was only one river, the Tocathins, that had these brightly colored irwini, but you seem to imply that maybe all Brazilian irwini would be similar?