  We propose a new form of the colour-kinematics/double-copy duality for
heavy-mass effective field theories, which we apply to construct compact
expressions for tree amplitudes with heavy matter particles in Yang-Mills and
in gravity to leading order in the mass. In this set-up, the new BCJ numerators
are fixed uniquely and directly written in terms of field strengths, making
gauge invariance manifest. Furthermore, they are local and automatically
satisfy the Jacobi relations and crossing symmetry. We construct these BCJ
numerators explicitly up to six particles. We also discuss relations of the BCJ
numerators in the heavy-mass effective theory with those in pure Yang-Mills
amplitudes.
