Dark spots on white cat’s ear

My flat mate adopted a lovely white cat named Toad yesterday! The rescue we adopted her from didn’t think she had any problems, but warned us to be very careful about her sun exposure, especially because the New Zealand sun is really harsh (thin ozone).

So her ears have these little dark spots on them and I’m just worried that they might be the beginning of a skin problem. We’re watching them to see if they change at all and if they do we’ll take her to the vet. Any other advice?