These look like they are made of fondant, gumtex or a combination of them mixed together.
If you google 'fondant rose tutorial" you can see some videos on how they are made....it involves cutters for different size petals, a couple of foam mats and a ball tool ( it makes the edges thin and ruffled.)
They take a bit of practice to get them to look delicate, but I've seen some gorgeous on here from the ladies that take the time to perfect it.
You can also buy premade ones if you don't have time to make them, try caljava or look on etsy. You could buy them in white and then buy luster dust to dust them the exact shades you wanted...it looks nice to have the center of the rose darker than the petals.
Good answer Texas Rose!
The variety available on line is awesome. Every shade and combination you can dream up to make a simply gorgeous cake.