Add measurement plugins that use the new coadded transmission curves to report the relative contributions from different filters (e.g. i vs. i2) for each object, and something like per-object color terms that would allow the object's photometry to be corrected to a pure r2-i2 system.

I think we'd want to defer actually correcting the photometry to DB load, as a measurement plugin that modifies the outputs of other plugins is messy and makes debugging harder.