  Instruments such as the ROTSE, TORTORA, Pi of the Sky, MASTER-net, and others
have recorded single-band optical flux measurements of gamma-ray bursts
starting as early as $\thicksim$ 10 seconds after gamma-ray trigger. The
earliest measurements of optical spectral shape have been made only much later,
typically on hour time scales, never starting less than a minute after trigger,
until now. Beginning only 58 seconds after the \emph{Swift} BAT triggerred on
GRB201015A, we observed a sharp rise in optical flux to a peak, followed by a
power law temporal decay, $\propto t^{-0.81 \pm 0.03}$. Flux was measured
simultaneously in three optical bands, g\p, r\p, and i\p, using our Burst
Simultaneous Three-channel Imager (BSTI) on the NUTTelA-TAO telescope. Our data
during the decay show strong colour evolution from red to blue, with a change
in the optical log slope of $+0.72 \pm 0.14$; during this time the X-ray log
slope remained constant. We did not find evidence for a two-component jet
structure or a transition from reverse to forward shock or a prompt emission
component that would explain this change in slope. We find that the majority of
the optical spectral slope evolution is consistent with a monotonic decay of
extinction, evidence of dust destruction. Assuming a constant source spectral
slope and an SMC-like extinction curve, we derive a change in the local
extinction $A_\mathrm{v}^\mathrm{local}$ from $\thicksim$0.8 mag to 0.3 mag in
$\thicksim$2500 seconds. This work shows that significant information about the
early emission phase is being missed without such early observations with
simultaneous multi-band instruments.
