the marketing material say that there be a option to select between blue or red light number - red be the only choice . it be suppose to have a battery backup but when the cord be pull from the outlet nothing display , however , the clock have keep time when electrically re-powered . several new high-quality 9 volt battery be use to perform the test to confirm that the battery be not the problem . I would give 3-star for the large letter and ease of operation .