Mitch, as you know there are multiple NOAA websites. Buried in one of them is a chart legend. Rotsa Ruck finding it. The Glaim and ASA manuals have some good basic explanations as well. You might contact the publications (outreach) section below - my guess is they'll be initially baffled, but they might be able to find something.
NOAA - National Oceanic and Atmospheric Administration - Contacts
Reviewing my earlier post - the scale on the left denotes the wind speed shading. If there were an area where winds exceeded 150 knots, for example, you'd see purple.