  Pair production of colored particles is in general accompanied by production
of QCD bound states (onia) slightly below the pair-production threshold. Bound
state annihilation leads to resonant signals, which in some cases are easier to
see than the decays of the pair-produced constituents. In a previous paper
(arXiv:1204.1119) we estimated the bound state signals, at leading order and in
the Coulomb approximation, for particles with various spins, color
representations and electric charges, and used 7 TeV ATLAS and CMS resonance
searches to set rough limits. Here we update our results to include 8 and 13
TeV data. We find that the recently reported diphoton excesses near 750 GeV
could indeed be due to a bound state of this kind. A narrow resonance of the
correct size could be obtained for a color-triplet scalar with electric charge
-4/3 and mass near 375 GeV, if (as a recent lattice computation suggests) the
wave function at the origin is somewhat larger than anticipated. Pair
production of this particle could have evaded detection up to now. Other
candidates may include a triplet scalar of charge 5/3, a triplet fermion of
charge -4/3, and perhaps a sextet scalar of charge -2/3.
