  We study the impurity physics at a continuous quantum phase transition from
an SU(3) symmetric N\'eel ordered state to a valence bond solid state that
breaks lattice symmetries, using quantum Monte Carlo techniques. This
continuous transition is expected to be an example of `deconfined criticality'
in an SU(3) symmetric system. We find that the spin-texture induced by a
missing-spin defect at the transition takes on a finite-size scaling form
consistent with expectations from standard scaling arguments at a
scale-invariant quantum critical point, albeit with significant subleading
power-law finite size corrections that we analyze in detail. Together with
recently-found logarithmic violations of scaling at similar continuous
transitions in the SU(2) case, our results provide indirect evidence for the
existence of operators that become marginal as $N$ is reduced to 2 in the field
theoretical description of these deconfined critical points.
