Although I always groan about making them (they really are a pain), white macarons do have a uniqueness to them.
These are lychee flavoured - using a generous splash of Soho Lychee Liqueur in a white chocolate ganache. I have tried using lychee juice and/or chunks of lychee but the flavour is never intense enough without the Soho.
For the macaron shell recipe, see my old post here.
The trick to keeping them white is to bake at 100 degrees celsius rather than 150, and bake for an extra 5 minutes (I kept mine in for 18 mins instead of the usual 13).