  Multiband photometric transit observations (spectro-photometric) have been
used mostly so far to retrieve broadband transmission spectra of transiting
exoplanets in order to study their atmospheres. An alternative method was
proposed, and has only been used once, to recover broadband transmission
spectra using chromatic Rossiter-McLaughlin observations. We use the chromatic
Rossiter-McLaughlin technique on archival and new observational data obtained
with the HARPS and CARMENES instruments to retrieve transmission spectra of HD
189733b. The combined results cover the widest retrieved broadband transmission
spectrum of an exoplanet obtained from ground-based observation. Our retrieved
spectrum in the visible wavelength range shows the signature of a hazy
atmosphere, and also includes an indication for the presence of sodium and
potassium. These findings all agree with previous studies. The combined visible
and near-infrared transmission spectrum exhibits a strong steep slope that may
have several origins, such as a super-Rayleigh slope in the atmosphere of HD
189733b, an unknown systematic instrumental offset between the visible and
near-infrared, or a strong stellar activity contamination. The host star is
indeed known to be very active and might easily generate spurious features in
the retrieved transmission spectra. Using our CARMENES observations, we
assessed this scenario and place an informative constraint on some properties
of the active regions of HD 189733. We demonstrate that the presence of
starspots on HD 189733 can easily explain our observed strong slope in the
broadband transmission spectrum.
