I have one of these and have recently asked the same question on several forumms. it seems that it is a medium ie 200 gm filling. but it does look thicker and heavier than that. I've just bought a second hand full neck version off eBay and the seller stated it is 370gm hevy weight so maybe they did both weights in that colour.
I have the green checked one and thats definately medium (200g) as I only took it out of the bag the other day. I thought the blue one was heavyweight?? One thing I didnt like about it though was one of the front fastenings came undone. Think its due to the new velcro closure on them as it stops any pressure on the front clasps that I think is needed to keep them fastenned. Anyone else had a problem.
Well i have a blue checked one and a green checked one and they are both light weights - no filling!! Think they just change the colour every so often!!