  Here we present additional photometry of targets observed as part of the
Hubble Wide Field Camera 3 Test of Surfaces in the Outer Solar System. 12
targets were re-observed with the Wide Field Camera 3 in optical and NIR
wavebands designed to compliment those used during the first visit.
Additionally, all observations originally presented by Fraser and Brown (2012)
were reanalyzed through the same updated photometry pipeline. A reanalysis of
the optical and NIR colour distribution reveals a bifurcated optical colour
distribution and only two identifiable spectral classes, each of which occupies
a broad range of colours and have correlated optical and NIR colours, in
agreement with our previous findings. We report the detection of significant
spectral variations on 5 targets which cannot be attributed to photometry
errors, cosmic rays, point spread function or sensitivity variations, or other
image artifacts capable of explaining the magnitude of the variation. The
spectrally variable objects are found to have a broad range of dynamical
classes, absolute magnitudes, exhibit a broad range of apparent magnitude
variations, and are found in both compositional classes. The spectrally
variable objects with sufficiently accurate colours for spectral classification
maintain their membership, belonging to the same class at both epochs. 2005
TV189 exhibits a sufficiently broad difference in colour at the two epochs that
span the full range of colours of the neutral class. This strongly argues that
the neutral class is one single class with a broad range of colours, rather
than the combination of multiple overlapping classes.
