Well, since I was somehow directed here.. I gotta say you gotta it all wrong.
Propylene has more pressure than propane. That means, Map Pro (yellow cans) can withstand lower temperatures than Propane (blue cans) / green gas.
I'll leave some links to technical vapour pressure charts about the three main gases for airsoft:
"Green gas" airsoft guns are designed to operate about 80 to 170 PSI range. That means:
* about 25ºC to unrealisticly hot 50ºC for 134A
* 12ºC to 37ºC for propane / green gas
* 4ºC to 29ºC for propylene.
The lower you go on the temperature range for a given gas, the more volume it will take for each shot, and thus, the least gas millage. Theoretically, in a perfectly sealing gun you can go even lower, as far as the pressure is enough to overcome the atmospheric pressure (about 14PSI) + the strenght of the springs. I've used Propylene at -2ºC (65PSI) on a WE AK without major issues other than high gas consumption, and that thing has a heavy bolt, strong recoil spring and perhaps the longest bolt travel distance in all airsoft.
Going higher than that range can and will produce damage to the seals in most guns, perhaps the only notable exception being the GHK M4 mags. Those beast can handle injected CO2, which is insanely hot.
BTW, never, ever, ever try to inject CO2 in green gas mags (unless it's GHK M4 with DevilHunter's mod). CO2 has at least 5 times the pressure the mags are designed for, and the mags will bloat and fail beyond any possible repair. Sounds like an abvious advice, but as a GBB tech I've received many, many mags on the "I don't know why, it keeps leaking" excuse, only to later find out they have injected CO2 and the metal walls of the mags are literally bloated.
Plastic slides guns such as some KSC and Marui work at lower pressures as they have to defeat way less weight, so 60 to 100 PSI is normally more than enough.
As for red gas, black gas and such designations, cannot provide specific data unless someone knows the real gas composition (as in "green gas is propane")
Going into experimental territory, for those cold times when not even Propylene is enough, the newest kid in the block of refrigerant gases shows great potential.
The theoretical range for R32
in a "green gas" mag would be -8ºC to 14ºC, so it should work perfectly for those scenarios on which people normally would go for CO2 mags.
So if anyone feels like trying their chances.... I would do that myself, but R32 is not yet available in my country. That's a first world kind of thing
As for the flammability discussion, all refrigerants are either flammable, toxic, global warmers or ozone depleters. So really, flammability doesn't sound that bad.