  In this talk we review relations and representations of primitive QCD tree
amplitudes. Topics covered include the BCJ relations, the CHY representation,
and the KLT relations. We will put a special emphasis on how these relations
and representations generalise from pure Yang-Mills theory to QCD. The
generalisation of the KLT relations from pure Yang-Mills to QCD includes the
case of massive quarks. On the gravity side we then obtain hypothetical
particles interacting with gravitational strength, which can be massive and
non-relativistic.
