Final answer:
The '50' in the Grey't Naturals collection could refer to various marketing or product-related details, but without specific context, it's not possible to provide a clear answer. Contacting the company or referring to their product information would be recommended.
Step-by-step explanation:
The question regarding what the '50' stands for in the Grey't Naturals collection seems to pertain to a specific product line or brand rather than an academic subject. This question would likely require specific knowledge about that product line or the marketing context in which '50' is being used. It may refer to an ingredient concentration, a product number, or a marketing slogan specific to the Grey't Naturals brand.
If this is related to a schoolwork question, it would likely fall under a business or marketing category, but without further context, it's not possible to provide an accurate answer. To obtain a precise explanation, it would be best to contact the company directly or refer to their official product information.