Im curious about the silicone, where did you find that info?
http://www.garagejournal.com/forum/showthread.php?t=33602
but a little after I read that I searched a little more and found this on another forum
The following is from permatex....
color.....................special property......max temp..........applications
Red........................High temp...............650*F....Valve covers, oil pans, timing covers, water pumps, thermostat housings, transmission pans
Blue.....................sensor safe...............500*F...Valve covers, oil pans, timing covers, water pumps, thermostat housings, transmission pans
Orange.......Sensor safe AND High temp....650*F...Valve covers, oil pans, timing covers, water pumps, thermostat housings, transmission pans
Ultra-Black.........Max oil resistance.........500*F....Valve covers, oil pans, intake manifold end seals, timing covers, transmission pans ALSO sensor safe and fast curing
Ultra-blue............Sensor safe................500*F...Valve covers, oil pans, timing covers, transmission pans, differential covers
Ultra-copper.........Max temperature.........700*F... Exhaust manifolds/ headers, valve covers, oil pans, timing covers, water pumps, thermostat housingsAlso sensor safe
Ultra-grey.....High-torque/high-vibration..500*F.....Valve covers, oil pans, intake manifold end seals, timing covers, water pumps, thermostat housingsdoes not say sensor safe
In reality, for 90% of applications, they can be interchanged. But there are "slight" differences and it is alot of marketing to give customers choices.
A few more notes:
all of the "ultra" RTV's are second generation. Supposed to have better flexibility and seal ability. The Non-ultras are first-gen.
All of them except Ultra-copper and Ultra-grey say they can be used on Transmission pans. But I would NEVER use a silicone on a transmission pan. EVER.
Ultra-black and Ultra-blue dont list water-pumps and thermostat housings for an application. So maybe the coolant does something???
Ultra-copper is the only one listed for exhaust manifolds. Allthough I would never use just a silicone for an exhaust manifold.
Red and ultra-grey are the only two not listed as sensor safe.