Here is the decode:
Surface Lowest Cloud
Colour State vis Km (nm) base 3/8 or more
Blue 8(4.3) 2500 ft agl
White 5(2.7) 1500 ft agl
Green 3.7(2) 700 ft agl
Yellow 1.6(1) 300 ft agl
Amber 0.8(0.5) 200 ft agl
Red <800m
Black Not usable for other reasons
BS