If by mellow you mean less strident highs and upper mids, then IMO no, the RS1 is not for you. You should look into the RS2 and HF1 in that case, and consider investing in some vwap pads or flat pads as well (or you could just reverse the stock bowls). Both of these headphones are darker in balance and will have more pounding bass than the RS1. However, the RS1's bass will be tighter and snappier if that's a factor for you. Don't underestimate the difference pads make - the RS2/HF1 with flat pads are flat out DARK (vwaps and reverse bowls strike more of a balance).
In case by mellow you mean a slightly larger soundstage presentation than other Grados, then yes, they might be for you. The RS series will have more resolution than the HF1, but the latter sure was a deal back when it sold for $200 new.