Hi, I employ receptionists. I agree with eeyore. Pop along. Try to wear something similar so they think you already are in the mould of what they might be looking for.
If in doubt eg shes in trainers and keep fit gear if a gym, they wont be expecting you to do the same. Id go for a basic skirt/trousers/jacket option in a non-descript colour eg black, blue etc. It doesnt need to be a shirt, you could wear a slim fit tshirt underneath. Colour is fine, just keep to one and eg if red use it throughout the outfit. So red top, red hair band, red handbag. It gives the impression of a uniform without being one. Id suggest tights as they look more professional and it depends on the desk you are working at as to whether legs are on show or not.
Hint: receptions often look for tricks to be shown. Dont wear nail varnish. Often this is banned in an outfit because fingers are on show. Wear very small jewellery and not dangly earrings. Wedding rings are ok, but avoid very obvious chains or if so keep it simple and smart. Less is definately more here. Keep your hair tidy and ensure your bag goes with the outfit. Dont ruin a great outfit with a denim handbag for example. They expect a package.
Finally sit up straight and look interested. Sounds idiotic but Ive met some great people standing up that look flipping awful sitting down because they slouched and got too comfortable and it looked messy. If its reception you are going for you have to carry that demeanour all the way through the interviews.
Best of luck! Hope you knock them dead! :0)