See
Military Colour Codes for METARs by Irv Lee for a simple, clear explanation of UK military weather colour codes.
NATO weather coding is dealt with in AWP 4(A). You can find a detailed description of the standard NATO airfield weather colour codes in Annex D, together with details of national variations. If I can find a link, I'll add it later.
Cheers
Here you go, but you may find it takes a while to d/l - seems to stick around halfway in
http://www.futenma.usmc.mil/wx/PUBS/AWP-4CH4.pdf
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and LIPX is combined CIV/MIL.