Magical cloaks which conceal the wearer, apparently by changing color or pattern.
Notes and interesting facts:
chameleon = lizards which can change the color of their skins for camouflage
While having chameleon cloaks could work on the Quidditch pitch because the other team could not see the players (only the stadium and crowd behind them), it is likely that they would be quite quickly banned by the International Confederation of Wizards Quidditch Committee as an unfair practice, because they give the cloaked team an unequal advantage over their opponents.
Although the date printed on the Daily Prophet Newsletter DP1 is 31 July 1998, the timeframe for that event is 1992-1993.