It's light blue, but also can be red (as red was the "general" color for the Osttruppen). There were different types of these tabs. I would go for the "right" light blue variant.
Here's some info: the first type of the Osttruppen tabs\boards was approved with an order № 2380/42 on 2th June 1942. You can see it here
http://blockhaus.ru/forum/index.php?showtopic=21230Later the situation changed again. According with the order of the OKH № 14124/43 on 29th May 1943 colorful tabs of the Eastern legions were changed for the grey tabs with just pipping. Shoulder boards also changed, but we're speaking about the collar... These tabs can be see here
http://sammler.ru/index.php?showtopic=99982&st=0 and on the pic from the Littlejohn's book.
Get yourself David Littlejohn's book on the Foreign legions of the Third Reich. Here's the pic from it.
http://i50.tinypic.com/1hutch.jpgGuys on the photo are wearing the second type of the Eastern insignia, since it's late 1943 or spring-summer 1944 and it's Western Europe. In the real life, Eastern volunteers were wearing anything - from pure German insignia to their own national one.
Lots of info and pics can be found here
http://reibert.info/forum/showthread.php?t=23465