  We present a large dataset of high cadence dMe flare light curves obtained
with custom continuum filters on the triple-beam, high-speed camera system
ULTRACAM. The measurements provide constraints for models of the NUV and
optical continuum spectral evolution on timescales of ~1 second. We provide a
robust interpretation of the flare emission in the ULTRACAM filters using
simultaneously-obtained low-resolution spectra during two moderate-sized flares
in the dM4.5e star YZ CMi. By avoiding the spectral complexity within the
broadband Johnson filters, the ULTRACAM filters are shown to characterize
bona-fide continuum emission in the NUV, blue, and red wavelength regimes. The
NUV/blue flux ratio in flares is equivalent to a Balmer jump ratio, and the
blue/red flux ratio provides an estimate for the color temperature of the
optical continuum emission. We present a new "color-color" relationship for
these continuum flux ratios at the peaks of the flares. Using the RADYN and RH
codes, we interpret the ULTRACAM filter emission using the dominant emission
processes from a radiative-hydrodynamic flare model with a high nonthermal
electron beam flux, which explains a hot, T~10,000 K, color temperature at
blue-to-red optical wavelengths and a small Balmer jump ratio as are observed
in moderate-sized and large flares alike. We also discuss the high
time-resolution, high signal-to-noise continuum color variations observed in YZ
CMi during a giant flare, which increased the NUV flux from this star by over a
factor of 100.
