The colour states are as follows:
Colour = Cloudbase (ft agl)/Vis
Blue = 2500/8km
White = 1500/5km
Green = 700/3.7km
Yellow1 = 500/2.5km
Yellow2 = 300/1.6km
Amber = 200/0.8 km
Red = anything less than amber!
Oh, and theres also Black, which means the runway is unuseable for reasons other than cloudbase or vis!
HTH,
Blunty