If you have full control over a Facebook page, you can manage access for other people or delegate certain tasks related to the page. You can add, edit or revoke someone's access to the page at any time.
Access to the page cannot be granted to a gray account. If you want to grant someone with a gray account access to the page, they must access the page through their personal Facebook account or create a new account. You can then grant access to the new account.
Please remember that you will need to link into your page to effectively manage page access You have the option to grant Facebook access to someone who has either full control or partial control of a page. People with Facebook access at either level can enter the page and effectively manage it on Facebook.