Thank you.
Thank you.
This answer kills the idea of *all* gases being invisible, with a picture to confirm:
TVP45: "Chlorine and bromine are quite visible, although you don't really want to check."
http://newsimg.bbc.co.uk/media/images/40155000/jpg/_40155431_gas2_203.jpg
And this answer...
I found this: https://www.physicsforums.com/showthread.php?t=105106
But it the question was never really answered there. So I'd like to ask a *similar* question again.
Are there any gases at STP, (without being "excited" or "liquefied"--see other topic, above) that are visible to the naked...