I don't think this has anything to do with digital formats. Rather, it may refer to the industry- or company-wide accepted convention on formatting printed labeling profile documents.

It's a normal practice to present product information/product labeling information in a structured way, including highlighting different sections of information with shading. So, I wouldn't be surprised if the practice is to have [product] annotations shaded, thus making them appear in grey boxes.

For example a drug name could be presented in large bold letters, its generic name(s) - in a smaller regular font, dosage options - in italic, and its annotation - in a grey box.