Currently the documentation for some of the color laws (e.g., F99, Cal00, CCM89) says that they return E(B-V).
If I'm not mistaken, these actually give the ratio A_lambda / A_V, where A_lambda is the extinction in magnitudes at the input wavelength and A_V is the extinction in V band. A_V can be computed as R_v * E(B-V), where E(B-V) can be looked up via SFD98Map for Galactic extinction. Could you correct these docstrings?