According to Achtung Panzer, the tubular type, as you have, were blue. But looking at a restored example as seen here, they are green;
The four lenses on the earlier type were green, so does anyone have a color photo of a blue one? I've seen lots of models with blue ones, but that doesn't mean it's correct....
Vintage photos appear as if there is not a cover over the tube;
General consensus seems to be that they were blue, but it's hard to argue a modern color photo, unless the part in this photo is totally wrong, or we have more than one variation of this type of convoy light.
Osprey's; Modelling the Panther Tank, has it painted blue also. A large color plate on page 56 of Squadron's Walk Around Sturmgeschutz III G depicts the light as a solid blue tube, without any covered divider as shown in the photo above.
Here is one on the back of a Hetzer;
So obviously there was more than just one type of the cylindrical ones, at least three!
Take your pick....