Would this violate racism laws?

I'm trying to set up a business selling skin care products and beauty treatments. My advertising budget is quite small so I was thinking of putting posters up in the college where I train (as a beauty therapist) asking for models that I can use in the advertising literature and on the website.

I want my advertising to show that the treatments and products that I sell are suitable for all different skin types so I was hoping to use about 4 or 5 models with different skin tones. If the models that respond to my advert are all white would it be legal for me to put up a new poster advertising for black and asian models or would that violate racism laws?

I suspect that it might but I can't afford to hire professional models and when I was modelling myself (many years ago now) I used to (when I was first starting out) do similar jobs to this myself where I wouldn't get paid but I would get a copy of the photographs to use in my portfolio.

The city where I train has very few black or asian people. My best friend is black and she's gorgeous but she isn't interested in being my model! My husband is Asian but he's a man and all of his friends are men and none of them are married or have sisters in this country!