3915 police bike

2 x policebikes


Here are 3 pictures. The first is the 3915 Police motorcycle. The other pictures are 2x 3986 police motorcycles.
They seem to be the same, HOWEVER the right hand motorcycle has a much lighter blue livery then the left one.
The frame is the same dark colour, only the livery on the body is different.
I have about 8 or 9 of these motorcycles, and 2 are lighter then the others.
Doe anybody know why or how? Is there a difference in one of the sets? Or would this be the 7681 rerelease through DS?
Sofar, i have seen this bike produced in the following sets:
3986
3915
4157 (advent)
4086 (megaset)
7681
I have the first three MISB, but they are all dark-coloured blue ones. The latter 2 i don't know.
Anyone?