osteospermum variety recommendation

Hi,

I have a very hot dry border, that seems to suit South African plants, almost exclusively. I've managed to establish some roses in it, which I love. They are yellow, orange and red. I underplanted with osteospermum, which grows like a weed and flowers incessantly from spring to autumn. Unfortunately the osteospemum is purple, which really clashes with the roses. I wondered if anyone could think of a really vigorous variety of osteospermum (like tresco purple) that is white or a really clean yellow, so as not to clash with the roses? Any recommendations of sun loving ground cover perennials also appreciated. 

Thanks!

Jen