  We consider fractional quantum Hall states in systems where two flat Chern
number $C=\pm 1$ bands are labeled by an approximately conserved 'valley' index
and interchanged by time reversal symmetry. At filling factor $\nu=1$ this
setting admits an unusual hierarchy of correlated phases of excitons, neutral
particle-hole pair excitations of a fully valley-polarized `orbital
ferromagnet' parent state where all electrons occupy a single valley. Excitons
experience an effective magnetic field due to the Chern numbers of the
underlying bands. This obstructs their condensation in favor of a variety of
crystalline orders and gapped and gapless liquid states. All these have the
same quantized charge Hall response and are electrically incompressible, but
differ in their edge structure, orbital magnetization, and hence valley and
thermal responses. We explore the relevance of this scenario for Moir\'e
heterostructures of bilayer graphene on a hexagonal boron nitride substrate.
