User Selectable Buttons That Express State

[Andrew H]

I apologize for the cryptic title. I wish to present a user with 12 small "buttons" (or little boxes), layed out from left to right in a table cell, each representing one of the 12 months (each such "button" would contain a single letter to identify the month, with ambiguity resolved by "relative position" - the reader should know that the "J" for June is to the immediate left of the "J" for July, for example). I attach an image, representing generally what I am looking for.



I want to enable users to select a particular month (button) by clicking, and then to have the "button" change in some manner to express the selection, but without losing the letter. For example, the button could become "shaded", but not so much as to obscure the selected button. If possible, I would like to make it impossible for the user to select 2 or more buttons.

Any suggestions would be appreciated.