  We demonstrate coherent control of photoemission from a gold needle tip using
a two-color laser field. The relative phase between a fundamental field and its
second harmonic imprints a strong modulation on the emitted photocurrent with
up to 96.5 % contrast. The contrast as a function of the second harmonic
intensity can be described by three interfering quantum pathways. Increasing
the bias voltage applied to the tip reduces the maximum achievable contrast and
modifies the weights of the involved pathways. Simulations based on the
time-dependent Schr\"odinger equation reproduce the characteristic cooperative
signal and its dependence on the second harmonic intensity, which further
confirms the involvement of three emission pathways.
