In some recent testing by the BGA it appears that, if anything, anti
collision marking may actually make aircraft less easily noticable.

Most of the midairs that we have seen recently have been between sailplanes
that knew there was another aircraft in close proximity before the collision
happened and in several cases have been between sailplanes actively involved
in 'cooperative flying'. When two 'non-cooperative' pilots happen to end up
sharing a thermal they tend to do so with a very high degree of caution
about each others actions. When cooperative flying gets going it appears to
me that a degree of familiarity or complacency creeps in.

It appears to me that the guidance emerging here seems to be 'assume
nothing, if you loose sight of the aircraft you know to be close by, talk
quickly to clarify the sitation whilst increasing your seperation safely'.
Perhaps safe cooperative flying does need a much higher level of
communication. Perhaps pilots flying cooperatively should carrry FRS radios
to allow them to chatter continuously. As one poster has already noted,
cooperative flying is a form of advanced formation flying with continuous
formation breaks and reformates and without much of a plan. In that
situation you have to know what you are up to, what the other pilot is doing
and the actions to take when the script gets lost! I remember a talk given
by a member of a top formation aerobatics display team in which he said that
once an aircraft in the formation was not where it was expected to be, when
it was supposed to be there, the only option was to break away and resync
the whole operation.

I have witnessed 2 mid-airs, thankfully with only one fatality amongst my
fellow pilots. Both were in non-cooperative flying. Both could possibly
have been avoided by better observation.

Ian