Database of color wavelengths of minerals
This type of information is made available through the USGS Spectroscopy Lab.

There is a researchable database of their current spectral library with the appropriate information for each mineral signature (formula, sample_id, type and more). Here is an example of the signature for Hematite:



Further, there is an up to date publication accompanying the database titled USGS Spectral Library Version 7, available here.