Comment # 9 on bug 1186341 from Martin Wilck

https://www.x.org/archive/X11R6.8.0/doc/RELNOTES5.html

5.3. Composite exposes extra visuals

When the Composite extension is enabled via xorg.conf or the command line, a
new visual is created. This visual is different from the other visuals used by
X applications in that it includes an alpha component. It is used by the
compositing manager and other Composite aware applications.

Most X applications ignore this visual since it is not useful to them; however
some applications mistakenly try to use it, which will cause them to fail. An
environment variable, XLIB_SKIP_ARGB_VISUALS, was added to the X11 library to
hide this visual from applications that mistakenly try to use it. If an
application fails only when the Composite is enabled, try setting this
environment variable before starting the application.

Since Composite is not enabled by default, it is not expected that this issue
will be visible to most users.