  Any loop QCD amplitude at full colour is constructed from kinematic and
gauge-group building blocks. In a unitarity-based on-shell framework, both
objects can be reconstructed from their respective counterparts in tree-level
amplitudes. This procedure is at its most powerful when aligned with flexible
colour decompositions of tree-level QCD amplitudes. In this note we derive such
decompositions for amplitudes with an arbitrary number of quarks and gluons
from the same principle that is used to bootstrap kinematics - unitarity
factorisation. In the process we formulate new multi-quark bases and provide
closed-form expressions for the new decompositions. We then elaborate upon
their application in colour decompositions of loop multi-quark amplitudes.
