  We obtain multivalley dark soliton solutions with asymmetric or symmetric
profiles in multicomponent repulsive Bose-Einstein condensates by developing
the Darboux transformation method. We demonstrate that the width-dependent
parameters of solitons significantly affect the velocity ranges and phase jump
regions of multivalley dark solitons, in sharp contrast to scalar dark
solitons. For double-valley dark solitons, we find that the phase jump is in
the range $[0,2\pi]$, which is quite different from that of the usual
single-valley dark soliton. Based on our results, we argue that the phase jump
of an $n$-valley dark soliton could be in the range $[0,n\pi]$, supported by
our analysis extending up to five-component condensates. The interaction
between a double-valley dark soliton and a single-valley dark soliton is
further investigated, and we reveal a striking collision process in which the
double-valley dark soliton is transformed into a breather after colliding with
the single-valley dark soliton. Our analyses suggest that this breather
transition exists widely in the collision processes involving multivalley dark
solitons. The possibilities for observing these multivalley dark solitons in
related Bose-Einstein condensates experiments are discussed.
