Why not advertise as British but play up your heritage? This is what I have done to a degree, although have been a little vague about my heritage and talk about being an interesting mix of x, y and z.
I'm white British because I am 'white' and hold a British passport. However, my ethnicity actually puts me in a different ethic group and I often tick that option when filling in 'official' forms as I feel this identity is important and needs to be recorded. However, I choose not to advertise as that as it is something that can a) be fetishised and b) be targeted by hate groups and having had experience of this in my non-escorting life, I most certainly am not going to open myself up to this kind of abuse/the kind of client who is looking to tick someone off a list.