The instructions in Academy's 1/144 Luftwaffe Phantom mention a color 'stone gray'. I looked at a few phantom pics on the net and it looks like that's a sort of blue-gray or neutral gray. Is that accurate?

Also, while researching I noticed a number of patterns of different shades of gray. Is there a story behind which pattern was used at which time, or are they pretty much interchangeable?

Hello Chuck, the paints you should use depend of the color scheme, you will do, here are the correct shades and the Xtracolors numbers for the Norm 81 scheme, i assume you want to do:
RAL 7009 Grun Grau or X256
RAL 7012 Basaltgrau or X254
RAL 7030 Steingrau or X257
RAL 7035 Lichtgrau or X260
RAL 7037 Staubraun or X258
RAL 7039 Quarzgrau or X259
Here is also a great help:
http://ipmsstockholm.org/colorcharts/stuff_eng_colorcharts_germany.htm

Best
Bernd

This is really useful. Thanks.