Sinusoidal surface-relief gratings (SRGs) formed by microphase separated photoresponsive poly(dimethylsiloxane)-block-poly(methyl acrylate-co-disperse red 1 acrylate) (PDMS-b-P(MA-co-DR1A)) chains are investigated. Different PDMS-b-P(MA-co-DR1A) were prepared by a multi-step synthetic approach which overcomes the challenges inherent to the synthesis of well-defined PDMS-based block copolymers (BCPs) having a DR1A dye content up to 50 wt%. A sinusoidal SRG (amplitude ≈ 5 nm, wavenumber ≈ 315 nm) interferometrically inscribed onto a thin PDMS-b-P(MA-co-DR1A) layer exhibiting an out-of-plane cylindrical structure with a period of ∼34 nm is demonstrated. Such kind of “two-colored” multiscale patterned surfaces could be envisioned as guiding patterns to efficiently direct the self-assembly of a BCP upper-layer via a hybrid chemo-/grapho-epitaxial alignment of BCP features.