  A colored weak singlet scalar state with hypercharge 4/3 is one of the
possible candidates for the explanation of the unexpectedly large
forward-backward asymmetry in $t \bar t$ production as measured by the CDF and
D0 experiments. We investigate the role of this state in a plethora of flavor
changing neutral current processes and precision observables of down-quarks and
charged leptons. Our analysis includes tree- and loop-level mediated
observables in the K and B systems, the charged lepton sector, as well as the
$Z \to b \bar b$ width. We perform a fit of the relevant scalar couplings. This
approach can explain the $(g-2)_\mu$ anomaly while tensions among the CP
violating observables in the quark sector, most notably the nonstandard CP
phase (and width difference) in the $B_s$ system cannot be fully relaxed. The
results are interpreted in a class of GUT models which allow for a light
colored scalar with a mass below 1 TeV.
