When a cover is "wet" cleaned using solvents, water baths, etc. it's considered restoration. When a cover is "dry" cleaned using brushes, erasers, cloth, etc. it is not considered restoration.
Neither are like a press, but the wet leads to purple whilst the dry leads to blue (unless there's something hinky like a detached staple or a signature that's not been witnessed....then it it'd lead to a green (qualified) label.
That's my understanding, but I'm not an expert. I'm sure there are a billion folks here more knowledgeable than I.
Thank you.