V Del is a Mira with a published spectral class of M4e. It has just passed through minimum. It typically shows color indices pretty typical for an LPV: (V-R) of +4.0, (R-I) of +3.0. However, on the current minimum, I've seen (B-V) go negative, while maintaining the strong red color in its other indices (B-V = -0.19, V-R = +4.17, R-I = +3.16). At first, I discounted these unusual B magnitudes due to the pretty poor SNR at the bottom of the lightcurve, but I'm realizing it isn't just one spurious data point.
Is there a credible physical explanation for one of these red stars to be unusually blue? I seem to remember that some of the H emission lines are located in the blue wavelengths. Can these intensify near minimum?