To largely repeat what I have posted elsewhere:
Most gliders are precluded from other than white finish because raised temperature from heat absorption weakens composite material.
I have asked the question about strobes for gliders in the past, and been told that they do not significantly aid visibility. Furthermore there are no approved modifications to fit them. While not impossible to overcome, that is a considerable hurdle for a fitment of dubious benefit.
The glint from wings is a huge signal compared with a strobe, though only effective when a glider is turning, and even that I find limited to a range of 1-2 miles.
High visibility fluorescent paint has been tried in controlled tests and found not to help - surprising, but true.
Batteries are a big problem for many - there is no room for more, and the weight limitation is already reached, on some, perhaps many, gliders. Even the 2-3 kg quoted above would put me over the limit in my glider. I also have no panel space, nor space elsewhere in the cockpit, for an extra box or two.
Could those who think solar power is the answer please look up what output you can get from a panel that would fit on a glider, and compare it with the power needed to drive a strobe or a transponder.
Personally I would welcome a workable solution. So far I am not convinced that there is one. I have no more wish to have anyone else fly into me from a blind spot than he/she has to do it. Statistically, however, GA/glider collisions are about the rarest form of accident. I can only recall two in over 30 years, and one of those was tug/glider in the vicinity of their home gliding site. Both power pilots and glider pilots have found far more prevalent ways of killing themselves.
Chris N