Flash Player does not support UPnP.
i would be interested in seeing your results of the test at http://cc.rtmfp.net
there are only two cases in which UPnP would make any difference for RTMFP communications:
1) your NAT is symmetric by default unless UPnP is used, in which case it becomes a flavor of cone NAT for that translation, AND your colleague is behind a symmetric NAT or port-restricted cone NAT
2) your network topology is double-NATed, you want to communicate with someone beyond your inner NAT but inside your outer NAT, and the outer NAT doesn't do hairpinning
my colleague is on a computer directly connected to the internet and i am behind a wifi home router connected to the internet with nat and upnp. there is no double nat involved here.
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the output of CC suggests that your NAT is a "kinda-symmetric* NAT" kind, where perhaps if you use UPnP it is no longer symmetric.
your colleague must have a port-restricted firewall that is blocking packets coming from you with a different source port than what your colleague expects (since your symmetric NAT has different outbound port translations for each destination endpoint).
if your colleague didn't have a firewall (or port-restricted cone NAT), you would be able to communicate since the situation would be exactly the same as communication with Stratus (to which you can connect).
* i say "kinda-symmetric" because *inbound* packets from foreign sources appear to be able to re-use an existing translation ("Can receive from same/different IP address, different UDP port number"), but *outbound* packets get a new translation for each distinct destination (the last "red/no" result).