  Production of electron-positron pairs by a high-energy $\gamma$ photon and a
bichromatic laser wave is considered where the latter is composed of a strong
low-frequency and a weak high-frequency component, both with circular
polarization. An integral expression for the production rate is derived that
accounts for the strong laser mode to all orders and for the weak laser mode to
first order. The structure of this formula resembles the well-known expression
for the nonlinear Breit-Wheeler process in a strong laser field, but includes
the dynamical assistance from the weak laser mode. We analyze the dependence of
the dynamical rate enhancement on the applied field parameters and show, in
particular, that it is substantially higher when the two laser modes have
opposite helicity.
