Fractional Chern insulators (FCIs) in ideal flat bands with Chern number C are commonly understood as color-entangled states constructed from C copies of the lowest Landau level. In realistic moiré systems, however, the band geometry is generally non-ideal, and the mechanism that stabilizes such FCIs remains unclear. Using twisted monolayer-bilayer graphene as a platform, we find two FCIs separated by a topological transition that occurs in a regime signaled by a local geometric instability of the Bloch states. Below the transition, the target C=2 conduction band is geometrically stable, and the resulting fractional phase is naturally described by the Halperin-(112) state. Above the transition, the system becomes geometrically unstable and enters a Laughlin-1/3 phase within the same target C=2 manifold, which persists even as standard quantum-geometry indicators degrade further. We attribute this Laughlin-1/3 phase to a hidden near-ideal C=1 component of the non-ideal C=2 Bloch states that becomes relevant under interactions, while its strongly non-ideal partner becomes irrelevant. We support this picture by applying a weak perpendicular magnetic field that acts as a ``color separator,'' directly visualizing the ideal subcomponent at the single-particle level. Together, these results clarify how non-ideal flat bands can stabilize FCIs, greatly expanding their parameter range and sharpening the role of quantum geometry in strongly correlated topological phases.