The Aqua Blue 3DS is to be discontinued, so if that’s the colour you where planning to buy then you should probably grab one quick.
According to Nintendo’s official hardware page (spotted by Andriasang) the system will soon be no more, although it’s not clear if this will apply just to Japan or Worldwide.
Currently you can pick up Aqua Blue, Cosmo Black, Flare Red, Misty Pink and Ice White. Japan also has an exclusive Cobalt Blue variant, which may well be the reason Aqua is making way.
The new Midnight Purple 3DS is the next colour to arrive, although as far as we are aware, this one is exclusive to the US for now.