RN color curves. We see that the RNe generally do not have strong color evolution. Nevertheless, three of the curves have
apparent reddening from the left to the right side of this plot. Two of these are the case of T CrB and RS Oph for which the
blue nova light becomes dominated by the red companion star light as the nova fades. (V745 Sco also is reddening systematically
through the observed portion of its eruption, but the horizontal range on this plot is limited, the change in color is fairly
small, and there are large uncertainties in the color evolution.) But the other case with a likely red giant companion (V3890
Sgr) has little if any color shift, although the resolution might be simply that the fading tails of the eruption were not
followed long enough. The other case with an observed reddening trend over much of its tail (CI Aql) does not have a simple
explanation that I know of. Color changes could easily be expected due to varying contributions from emission lines in the
B and
V bands which could change substantially throughout the eruption.