To color flat-color 3D models for illustrators, start by assigning solid base colors to each part via your 3D software’s material editor (e.g., Blender, Substance Painter)—avoid gradients to keep hues uniform.
Use layer-based workflows (like Vertex Paint or flat texture layers) to maintain clean edges, then export texture maps to 2D tools (e.g., Photoshop) to add subtle illustrative shadows or details without disrupting the flat look.
Stick to a limited color palette matching your illustration style for consistency, and test quick renders early to ensure flat colors translate well in 3D space.