We report direct measurement of spectrally selective absorption properties of PbSe and PbS colloidal quantum dots (CQDs) in Si nanomembrane photonic crystal cavities on flexible polyethylene terephthalate (PET) substrates. Enhanced optical absorption was obtained when CQD absorption overlaps with photonic crystal Fano resonances. On the other hand, no absorption was observed when the Fano resonance has no spectral overlap with the CQD absorption bands. The measurement results agree well with the simulation results obtained based on 3D FDTD and RCWA simulation techniques. Measured angular and polarization properties also agree well with Fano resonance transmission properties, which were obtained experimentally and, theoretically based on simulated dispersion properties and transmission properties. Bending induced spectral shifts were characterized for potentially flexible photonic device applications.