  Coherent diffractive imaging is a technique that recovers the sample image by
numerically inverting its diffraction pattern. We propose a generalization of
this method for the inversion of multi-wavelength data. Using this approach, we
show that separate reconstructions for each wavelength can be recovered from a
single polychromatic diffraction pattern. Limitations on the number of
wavelengths is provided by adapting the constraint ratio to the polychromatic
situation. The method's performance is demonstrated as a function of the source
spectrum, the degree of complexity within the exit wave and the sample geometry
using several numerical simulations. Lastly, an example shows the ability to
recover element-specific information using two harmonics selected from a
high-order harmonic generation source.
