While almost all roses have some degree of color variation, that's not what we mean when we say "multi colored".
Dark pink, fading to a paler shade on the edge of the petals does not qualify a rose to be on this page... only those with a definite and sharp color separation are selected.
A multi colored rose always attracts interest in the garden. It draws in admirers that would walk straight past a tradionally colored rose without a second glance. Something as flamboyant as Scentimental or Stars 'n Stripes is always going to be an attention seeker... they just scream out "look at me, look at me!"
For those of us that tend to be a little conservative in our gardens, these type of roses just don't fit in. Perhaps one here and there as a focal point, but too many just make the garden seem overly busy, it's hard to know where to look. Personally, I find the subtlety of blended colors much more pleasing to the eye. Just Joey for example. But of course, my opinion on bi colors doesn't count for anything, it's what you want to see in your garden that matters!
While it might be tempting to think that stripes are a reasonably modern addition to the rose family, that's not the case. While not common in the old Heritage roses, there has been some fairly popular examples. Honorine de Brabant and Variegata di Bologna are two that come to mind. Both bourbons, and both very fragrant.
But the oldest by far, is the well known Rosa Mundi (a sport of Rosa Gallica), and at over 450yrs this is one of the oldest of the species roses still grown. If I could have one striped rose and one only, this would be it, without a doubt. It is extremely fragrant, and very easy to propagate with cuttings. Being a Gallica, it's only once blooming, but I don't mind that in a rose. Somehow it manages to be everything the modern striped varieties aren't. It's showy without being pushy, easy to care for, and the frangrance is just devine. If you're looking for a striped rose (and if you can get it), I highly recommend this for your garden.
With the older varieties, it was all natural mutation. Almost all started as a sport of a none striped rose. But scientists being scientists, they feel the need to tinker and "improve" on nature, so some of the modern ones have been created with artificial genetic mutation. This can be irradiated or chemical alteration of the genes, which can produce all sorts of results... stripes being one of them.
However, the majority still come from either naturally occuring sports, or deliberate breeding programs that attempt to produce striped varieties. if you are going to try to produce a striped rose yourself, then probably the best variety to experiment with, is Ferdinand Pichard.
This Hybrid Perpetual (parentage unknown, Rémi Tanne France, 1921) has everything going for it, when it comes to use in a breeding program. Easy to grow, very disease resistant, fragrant, and it tends to throw up more than its fair share of striped progeny.