  The surface characterization of Trans-Neptunian Binaries (TNBs) is key to
understanding the properties of the disk of planetesimals from which these
objects formed. In the optical wavelengths, it has been demonstrated that most
equal-sized component systems share similar colors, suggesting they have a
similar composition. The color homogeneity of binary pairs contrasts with the
overall diversity of colors in the Kuiper belt, which was interpreted as
evidence that Trans-Neptunian Objects (TNOs) formed from a locally homogeneous
and globally heterogeneous protoplanetary disk. In this paradigm, binary pairs
must have formed early, before the dynamically hot TNOs were scattered out from
their formation location. The latter inferences, however, relied on the
assumption that the matching colors of the binary components imply matching
composition. Here, we test this assumption by examining the component-resolved
photometry of three TNBs found in the Outer Solar System Origins Survey: 505447
(2013 SQ99), 511551 (2014 UD225) and 506121 (2016 BP81), across the visible and
J-band near-infrared wavelength range. We report similar colors within 2 sigma
for the binary pairs suggestive of similar reflectance spectra and hence
surface composition. This advocates for gravitational collapse of pebble clouds
as a possible TNO formation route. We however stress that several similarly
small TNOs, including at least one binary, have been shown to exhibit
substantial spectral variability in the near-infrared, implying color equality
of binary pairs is likely to be violated in some cases.
