I know that they used 72 dated mills bombs with the two types of aluminium base plug as we found loads of shrapnel fragments but marked with a very dark brown body and a yellow band, yellow being the Nato HE band marking like the WW2 green band used before.
We found no blue or violet marked shrapnel. The modern L series at the time was also used quite a lot together. May be the blue indicating practice, (its the same colour of practice blue), violet for experiment, both used together was most probably used in trials comparing the throwing functioning and practicality between the two types of grenade, showing how it would work with webbing or uniform as well.
I did notice that some L series levers at the bottom had a small hole at the end for a safety wire, i was told was there just incase a pin was accidentally pull and lever not secured, just as the modern Swiss grenade has with a safety clip which is removed before the pin or after, visa versa. The mills doesn't have this secondary feature and was used to compare. Not sure what the accident rate was with grenades where levers and pins were accidentally removed ie snagging etc.
Not sure if a violet marked grenade or other form of device used on a range to be blown in test experimentaion trials would be marked showing it has an explosive content ie marked in yellow, it would be strange not showing the device had a dangerous content, especially when you know the military are quite strict with safety. I have seen the L series in blue practice with violet markings may be these mills are the same but not completely blue as the practice L series, the mills being short lived at the time and the markings adequate.