Percy Jackson and Beckendorf used them while playing Capture the Flag, but were captured by Annabeth Chase daughter of Athena and Silena Beauregard daughter of Aphrodite. Emily is also a daughter of Aphrodite.
The armor blends in with the wearer's surroundings. It doesn't provide true invisibility, but it comes close as it can change the color of the armor to match the exact color(s) of the background it is set against. However, it is only effective from a distance.