Purple roses do exist, but they are a rarer rose color. To obtain a purple rose, different naturally occurring rose species must be crossbred. You can also make a white or pink rose into a purple rose with artificial dyes.
Some varieties of "hybrid tea" roses can be grown with light-purple hues. Cardinal Hume roses provide deeper purple tones than hybrid teas, but they are more difficult to grow.
Purple roses require specialized breeding, so they are more expensive to purchase at a florist. However, you can make a rose look purple by placing white rose cuttings in a mixture of water and purple food coloring. Within a day or two, the rose petals will become purplish.
While food coloring works for cut roses, it is not advisable for growing purple roses in a garden. To grow an entire bush of purple roses, you'll need to buy a rose species that is naturally purple.