For coloring 3D building models in Blender, the best tools are the Shader Editor (for material-based color) and vertex painting (for direct surface details).
The Shader Editor uses nodes like Principled BSDF to create realistic materials—such as brick, glass, or metal—with adjustable color and texture. Vertex painting lets you paint colors directly onto the model’s vertices, great for gradients or hand-painted accents.
If you’re new to Blender, start with built-in material presets or use texture atlases (combining multiple building textures into one image) to simplify coloring without complex node setups.