The "color" of the paste on the core was grey but a really thick layer (2mm at least), and since AS5 is grey as well I bet they couldnīt tell a difference at all. The paste on the ram/voltage regulators was white mixed with some type of cloth, but I guess you could carefully pull that junk off and store it somewhere and put it back in case you had to do a RMA.
Save temperature seems to be the one that doesnīt cause any artifacts. I heard from guys that were running 90C at load (and stock clocks) and didnīt see any artifacts in games or benchmarks but on hot days I was getting artifacts at 70C (and 660/2050) in some benchmarks but thats with the HR03+. Iīm pretty sure my voltage is holding me back and not really the heatsink.
As long as your card doesnīt cause artifacts or BSODs and goes above 90-100C, Iīm sure you are not doing any damage to it. I believe the same rule applies for the shader clock as well.