Certainly until 1996 [when my crystal ball, fir cone, seaweed and pass were impounded] the Met Office never added other than:
BLU WHT GRN YLO AMB RED to any actual or forecast.
BLK was an ATC/OPS prerogataive.
YLO was never subdivided.
"The Board" in NATO was not subject to national [met] variations, only military interpretations.
"The Board" at JHQ Rheindahlen was started a year before my arrival as a rostered senior forecaster in 1980. Lads were still p*ssing themselves a year later. The PMeto had decreed a "Colour Board" in ther office, maintained by assistant number 1.
PMetO ordered buttons, coloured, magnetic, r a y g w b. Also board, metal. Map, NATO NW Europe. Fablon. Adhesive.
This was duly botched up and the grand unveiling. Neither r, o, y, g, w, or b adhered to fablon on map on board.
PMetO "its an inverse square law, fablon/ map/ adhesive too thick!"
Duly adjusted.
r,a,y,g,w and b still bit the dust.
"Sir, what's the board made of?"
"Aluminium alloy of course"
PMetO replaced very soon after, as was board.
When I arrived they were still larfing.
Best thing since sliced bread thereafter.
"David, were you expecting reds in Denmark?"
Sh1t!