Trick photography giving the impression of long,straggly hair,probably. A lot of enhancements were going on at the time. 
I'm also going by the pic with just him and June. It looks like the more wirey,sandy/fair hair that grows more outward than it does lengthwise.
Also the " vanishing " hair on the end of the silencer could have been that of Nevilles' as that wasn't very long for it to have been " lost " in transit.A longer hair would have stayed put,if only to have coiled itself around the damn thing. 
I still can't visualise this long straggly hair. 
Do you agree with Bamber that Sheila was in the kitchen when the raid team broke in. Having shot herself once. She then walked upstairs and shot herself again. None of the raid team seeing her go upstairs.
Wait there. Was the rifle upstairs ? There has never been a report of a rifle being seen in the kitchen.
That means Sheila shot herself upstairs. Then went downstairs to the kitchen without the rifle. Then back up stairs after the raid team entered to shoot herself again.
Or shot herself downstairs in the kitchen. Went upstairs and left the rifle there. Then went back downstairs to the kitchen. Then went back upstairs after the raid team entered WHF to shoot herself again.
A lot of walking for a woman with a bullet in her neck. She also magically avoided getting vertical blood lines during her walk abouts.