As someone who's now used GAFOR in Austria, Germany and Slovenia, however, I'm still a little unclear about the GAFOR weather criteria used in SD. In each country, the colours used actually denote slightly - but significantly - different weather minima. There appears to be no consistency across the board. Some countries omit certain colours altogether. 

My question therefore is this: does SD simply follow the specific weather criteria used by the met office for each individual country in its GAFOR presentation, or does it use its own criteria, consistent and universal across all countries where GAFOR is shown on SD? 

The situation is not made any clearer by the absence of any legend anywhere on SD - at least as far as I can see - delineating what each colour represents. 'Marginal VFR', for instance, can mean different things in different countries.  

Any advice?  

GAFOR are created by the countries themselves, not by us. If we say a route or area is open, it's because the country has forecast it to be open. The "clear" state was invented by Germany and is only used by Germany.

I will ask my colleague to review the GAFOR section of the documentation to ensure we mention that different countries can use different minima in their calculations.