This is the rainbow flag with an added black stripe to be aware of AIDS called "Victory over AIDS" flag. See, for example, here and here. M. Schmöger, 26 August 2001
Black: AIDS awareness; this stripe will be removed, as soon as a cure is found against AIDS. M. Schmöger, 26 August 2001, (translating from EuroGay.net)
The Victory Over AIDS Flag modifies the rainbow flag by adding a black stripe at the bottom. Suggested by a San Francisco group, the black stripe commemorates those we have lost to AIDS. Sergeant Leonard Matlovich, a much-decorated Vietnam Veteran dying of AIDS, proposed that when a cure is eventually found the black stripes should be removed from all the flags and ceremoniously burned in Washington, D.C. M. Schmöger, 26 August 2001 (quoting from Jasewells.com)
The flag was used (photo) at Guatemala Pride 2011 (Orgullo Guatemala 2011). Note the unusually light shade of violet color, much lighter than the one used on the "ordinary" gay rainbow flags which can be seen on the same photo.
The same flag was used (photo) at the Guatemala Pride 2010 (Orgullo Guatemala 2010), although on the flag photographed at the event, violet stripe turned out to look almost white, so it probably could not be recognized without the later source. Tomislav Todorović, 7 September 2014
A variant of the rainbow flag for "leathermen." The two lower stripes (blue and black) refer to the respective colours of the leather pride flag.
Reportedly, gay leatheraficionados might also modify a rainbow flag to have a black stripe instead of a violet one. (However, this version might be confused with the "Victory Over AIDS" version of the rainbow flag, as they are similar.) M. Schmöger, 24 August 2001 Source: http://jasewells.com/gayicons/
Black color usually symbolizes mourning; Rainbow Flags with additional black stripe were used in Israel after the 2009 shooting in the Tel Aviv building of Agudah. One of those designs was a six-striped Rainbow Flag, charged with a black vertical stripe, visibly narrower than the rainbow stripes, placed near the hoist.[1]
Beside mourning, black can also symbolize protest; to signify that, black horizontal stripe was added to the center of a long Rainbow Flag (between yellow and green) which was carried by the participants of a rally against the Proposition 8 (the amendment to the Constitution of California, adopted in 2008 and eventually overturned in 2013, which restricted the right to marry to heterosexual couples), which took place in San Francisco on 4 August 2010. Tomislav Todorović, 21 June 2020 Source: SFGATE website: https://www.sfgate.com/bayarea/article/Rainbow-flag-turns-40-Gilbert-Baker-pride-parade-13015011.php#photo-2262779
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