Green and red are traditionally Christmas colors and it is almost December so maybe it means ..... SANTA'S COMING! :)
Actually, I'm not sure which platform you are asking about but on mine that would indicate that the ask is currently lower than the previous sales. In other words, a sale went off at 10.00 and since then, the ask dropped to 9.95 all trades at the ask are now lower and shown in red to indicate the price has come down.