I was having the same trouble with an LC smith 00 and fixed it by using a bit larger 4in diameter crucible as well as packing scraps of steel around the receiver without touching it. The scraps of steel I use are shaped similar to the side plates. I felt like the problem of getting mostly grey was because the coal was not staying around the receiver and air was coming in contact as it fell into the quench. By having a larger crucible there is more coal ensuring that it stays surrounded by coal as it cools in the quench as it drops. Someone I know recommend the steel scraps and it really made a difference as well as mimics the splash which probably occurred at the factory as I would expect they colored many receivers at one time. I am by no means an expert at this but have really learned a lot by trial and error and found this to help.
