It's always been the case.... When a console comes out it usually limited to either one or a couple of colours....... Later on - Nintendo then brings out other colours
IIRC when the DSPhat first came out, it was only available in silver - then you could get other colours,
the same for the DSi - that was only Black and White on release IIRC - now we have various other colours. The Wii - was originally only available in white - now we have Black and Red versions
I would guess it's the same for the 3DS - we'll start with the Blue and Black, then when a Mario game comes out - the red?? , Zelda game - the green ?? then other colours I would guess will come out