  Transmission spectra probe exoplanetary atmospheres, but they can also be
strongly affected by heterogeneities in host star photospheres through the
transit light source effect. Here we build upon our recent study of the effects
of unocculted spots and faculae on M-dwarf transmission spectra, extending the
analysis to FGK dwarfs. Using a suite of rotating model photospheres, we
explore spot and facula covering fractions for varying activity levels and the
associated stellar contamination spectra. Relative to M dwarfs, we find that
the typical variabilities of FGK dwarfs imply lower spot covering fractions,
though they generally increase with later spectral types, from $\sim 0.1\%$ for
F dwarfs to 2-4$\%$ for late-K dwarfs. While the stellar contamination spectra
are considerably weaker than those for typical M dwarfs, we find that typically
active G and K dwarfs produce visual slopes that are detectable in
high-precision transmission spectra. We examine line offsets at H$\alpha$ and
the Na and K doublets and find that unocculted faculae in K dwarfs can
appreciably alter transit depths around the Na D doublet. We find that
band-averaged transit depth offsets at molecular bands for CH$_{4}$, CO,
CO$_{2}$, H$_{2}$O, N$_{2}$O, O$_{2}$, and O$_{3}$ are not detectable for
typically active FGK dwarfs, though stellar TiO/VO features are potentially
detectable for typically active late-K dwarfs. Generally, this analysis shows
that inactive FGK dwarfs do not produce detectable stellar contamination
features in transmission spectra, though active FGK host stars can produce such
features and care is warranted in interpreting transmission spectra from these
systems.
