There are already quite a few JoyCon colours on the market. If you’re more of a plain or sleek guy, you can choose receive grey JoyCons with your Switch purchase, but if you’re more the colourful type, then there is Neon Blue and Red, Neon Yellow, or Neon Pink and Green you can choose from. Up until now, in Japan, if you wanted to have a mixture of different colours then the ones above, you would have to also purchase a separate pair of JoyCons with your brand new Nintendo Switch.
It seems that Nintendo of Japan’s website has now launched a Nintendo Switch JoyCon bundle builder of sorts. This tool lets you choose which colour you want each of your included JoyCons to be in, you can even choose what coloured straps your want. There is a slight catch however. At the time of writing, you may only choose colours which have been specifically released for that specific JoyCon. That means you will be able to get your left JoyCon in Neon Green, but you cannot get the right one in that colour as Nintendo have yet to officially release the right one in Neon Green.
This is a bit of a drawback, though I could see this pave the way for more customisable colour combinations in the future. Hopefully the service may find its way overseas soon.