First of all, Hermann Graf never commanded JG 2.
Secondly, none of the Fw 190s which he flew was all yellow.
Thirdly, Graf didn't fly any missions in the area where that all-yellow Fw 190 is said to have been seen.
Fourth, Graf was not shot down on the date - or even a date close to that date - when the all-yellow Fw 190 should have been shot down.
The whole story about Major von Graff/Graf commanding JG 2 "Richthofen" and flying an all-yellow Fw 190 originates from Pierre Clostermann's "The Big Show". In my book "Graf & Grislawski" (published in August 2003) I examined that closely.
See:
http://www.graf-grislawski.elknet.pl/index.htm
In the latest edition of "The Big Show" (published in 2004, with the foreword written in September 2003), Pierre Clostermann made this new addition regarding the pilot of the all-yellow Fw 190:
"Later we learned that it was not Graff, but maybe Oesau". (p. 50.)
If you want to build good and accurate models of any of Graf's Fw 190s, Claes Sundin has made great colour profiles of 26 different aircraft flown by Graf & Grislawski in the book with the same title, and Eagle Editions has printed decals to all of them. For a link to the decals, see the link above.