16. The computerized EDS server of claim 14 , wherein the computer processor: receives a search query expression provided by a user.
17. The computerized EDS server of claim 16 , wherein the EDS server translates the search query expression by the user to a covering-query on a set of color tags corresponding to the plain color-index, and is issued to the cloud-storage platform to search over a set of plain documents stored in a portion of the cloud-storage platform associated with the user.