The intrinsic colors of RR Lyrae variables: A means to determine interstellar reddening

We present refined BVI light curves for six field RR Lyrae variable stars. The refinements include new data and improved photometric calibration compared to our previous work. For each star, we derive the intensity mean magnitudes, light amplitudes, and colors at minimum light. We combine our results with literature data to estimate the mean dereddened RR Lyrae color at minimum light to be (V-I)(o,min) = 0.58 +/- 0.02 mag, with a star-to-star scatter of 0.024 mag. Any dependence of color on metallicity is too weak to be formally detected with the available data. One of our stars exhibits the Blazhko effect. The star's minimum light color is unchanged at the two observed phases of the star's Blazhko cycle, while the maximum light color changed significantly. This insensitivity further supports the reliability of minimum light colors as a tool for ( V - I) measuring interstellar reddening.