Why would removing eosin y and/or methylene blue from emb agar alter the medium's sensitivity or specificity/?

EMB agar is a selective medium for gram negative bacteria. It is a selective and differential medium for coliform. EMB agar contain eosin which is toxic to gram positive bacteria; the function of eosin is to inhibit the growth of gram positive bacteria and to react with lactose fermenter.

Eosin thus customize EMB agar for gram negative bacteria and removing it from the agar will alter the medium sensitivity.