Five Green. I believe the proposed limit is 10 msv units (Milli or Micro Sieverts??) and that, by calculation and projection, pilots AVERAGE about 2 - 3 msvs per year. The 6msv limit sounds sensible since you'd have reason to be grounded if you got to 9msv.
Can dosimeters be bought? How much? IIRC, there are different types depending on which types of radiation you are expecting to have to measure.
Britannia Airways did some measuring of radiation exposure a few years ago but I'm not aware of the results.