Old sample of sodium tetraphenylborate—why it is red?
According to Decomposition of Sodium Tetraphenylborate, which relates to the Savanna River site for nuclear weapons material production,


  Stable aqueous NaTPB solutions are a transparent,
  flesh-toned color. During the initial stages of decomposition (or
  instability),the solution turns a golden color. As the quantity
  of TPB- that has decomposed increases, the solution turns dark
  red, then brown, and eventually black.


In the presence of oxygen "phenol and phenylboronic acid
are produced as well as benzene, biphenyl, and other benzene ring
derivatives".