The LARGE majority of notable free-jazz musicians were black; both the leaders/trend-setters and "foot-soldiers". However, the music became more popular in europe than in the USA so you got a LOT of european, white guys playing it towards the mid-late 60's; some are legends today but it would be quite a stretch to put, say, Peter Brötzmann, Evan Parker, Derek Bailey or Ton Oxley on the same level as Ayler, Coleman, Taylor, late Coltrane, Sanders, Cherry, AEOC, Sun Ra, Anthony Braxton and numerous others in terms of status/impact/recognition etc.

Still, there's been lots of dope white free-jazzers (especially later) but I'm personally heavily biased towards US free-jazz and more avantgarde post-bop from the 60's so >I tend to gravitate more towards the black US musicians even if there were some dope white guys in the US as well (Charlie Haden, Paul Bley and Roswell Rudd comes to mind).

As for when *american* free-jazz became white, I don't think that really happened until the 80's; the 70's "loft-jazz" scene was still dominated by black musicians in USA (=David Murray, Braxton, Threadgill, Oliver Lake etc.)...EDIT:I guess it mirrors US jazz at large even if Wynton and the "young lions" led to a new generation of black musicians getting recognition for more "traditional" jazz. I think that might have played a part in free-jazz being viewed as more white musically but there's been some prominent Black free-jazz musicians coming out after the 80's even if I guess many of them still had roots in that 70's loft-scene. Still, Matthew Shipp, David S. Ware (who played with Cecil in the mid-70's but became a "name" later), Charles Gayle (yuck!) and a few others come to mind as fairly well-known examples...

Basically, the *audiences* might have been predominantly white (not sure about that either, as you said, many of the militant guys were into free-jazz) but the musicians were still predominantly black in the US...