In my experience, from 2 purple roses you'll only get purple roses. However, from 2 pink roses you might get a pink, a white or a red rose. From a white + white combination you can still get another white rose, so I think it'd be better to put 2 purple roses and a white and a red rose. I have bred a lot of pink roses that way, though you might still get red and white roses. Pink roses are a pain in the ass, at least to me, lol.