The key to limits on protection of architectural works in the US is the definition of the term in 17 USC 101:
An “architectural work” is the design of a building as embodied in any
tangible medium of expression, including a building, architectural
plans, or drawings. The work includes the overall form as well as the
arrangement and composition of spaces and elements in the design, but
does not include individual standard features.
The US Copyright office explains what this means in Circular 41, saying
The authorship in an architectural work includes the overall form of
the building — the exterior elevations of the building when viewed
from the front, rear, and sides — as well as any arrangement and
composition of walls or other permanent structures that divide the
interior into separate rooms and spaces. Copyright does not protect
the following elements:
Individual standard features of the architectural work, such as
windows, doors, or other staple building components.
Standard configurations of spaces, such as a square bathroom or
Purely functional features of an architectural work, such as
innovations in architectural engineering or construction techniques.
Interior design, such as the selection and placement of furniture,
lighting, paint, or similar items.
This explicitly excludes paint. Chapter 300 of the Compendium of U.S. Copyright Office Practices and especially ch. 900 goes into further detail of things excluded, such as "Common architecture moldings, such as the volute used to decorate Ionic and Corinthian columns", "Common patterns, such as standard chevron, polka dot, checkerboard, or houndstooth designs".