All platform members can label a grid's thumbnail (even if this is just within their own private grids in their own private folder area - for user and external member types).
An architect or builder can add/manage labels for a specific grid thumbnail in the main grid library.
Configurable access control will determine who has the access permission to add/manage labels for a specific grid thumbnail in the main grid library; see What is configurable access control?
First, it makes sense to define the grid labels you seek to use for your Method Grid account - as displayed in the grid library label legend. See How do I edit the label legend for all my grids?
Once this is done, you are set to add/manage labels for a specific grid thumbnail. This is done within the grid library page (displaying all the grid thumbnails). Now, in edit mode, you will see new action buttons revealed on each individual grid thumbnail. Select the label action button on the grid thumbnail that you seek to update.
You will note that this reveals a dropdown showing all labels with two vertical check box columns.
Selecting the check box in the first "Dot label" column adds that colour dot to the bottom of the grid thumbnail. De-selecting any previously assigned labels removes the label. You can add multiple such labels.
Selecting the check box in the second "Full label?" check box colours the entire grid thumbnail to that label's colour. You can only, therefore, select one such label as the primary label.
Once changes have been made, click the save/tick action button to save all changes out.