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We present a large dataset of high cadence dMe flare light curves obtainedwith custom continuum filters on the triple-beam, high-speed camera systemULTRACAM. The measurements provide constraints for models of the NUV andoptical continuum spectral evolution on timescales of ~1 second. We provide arobust interpretation of the flare emission in the ULTRACAM filters usingsimultaneously-obtained low-resolution spectra during two moderate-sized flaresin the dM4.5e star YZ CMi. By avoiding the spectral complexity within thebroadband Johnson filters, the ULTRACAM filters are shown to characterizebona-fide continuum emission in the NUV, blue, and red wavelength regimes. TheNUV/blue flux ratio in flares is equivalent to a Balmer jump ratio, and theblue/red flux ratio provides an estimate for the color temperature of theoptical continuum emission. We present a new "color-color" relationship forthese continuum flux ratios at the peaks of the flares. Using the RADYN and RHcodes, we interpret the ULTRACAM filter emission using the dominant emissionprocesses from a radiative-hydrodynamic flare model with a high nonthermalelectron beam flux, which explains a hot, T~10,000 K, color temperature atblue-to-red optical wavelengths and a small Balmer jump ratio as are observedin moderate-sized and large flares alike. We also discuss the hightime-resolution, high signal-to-noise continuum color variations observed in YZCMi during a giant flare, which increased the NUV flux from this star by over afactor of 100.

M Dwarf Flare Continuum Variations on One-Second Timescales: Calibrating and Modeling of ULTRACAM Flare Color Indices