White Short Two-Piece &
Elvis used a multicolored blue scarf to this suit, also know as "White Two-Piece Pocket" suit. This has been in display in Graceland and is now in their archives.
It is possible that Elvis used a "Navy Blue Short Two-Piece & Chest Pockets" suit, but is is very hard to see the difference between a black and a dark blue suit. Even if there exists some photos where the suit looks blue, it is believed that it is the stagelight and development of the photo that makes the color of the suit look blue.
Elvis Presley, Fashion for a King, by Tommy Edwardsen and Atle S. Larsen (Follow That Dream)