Having a jar of violet syrup on your bar shelf is always impressive, even if you don't drink alcohol. It's a conversation starter. It's beautiful. Its flavor is sublime.
I'm not blessed with the viola odorata in my yard, but that doesn't stop me from making concoctions with the mildly sweet and much more greenly-complex flavors of the viola sororia. In fact, I prefer it. My palate doesn't tend to enjoy overly floral flavors, so I don't bother to ID any violets. I just pick all the purple ones.
That's the key to the color: get the purple ones. The white ones I find are excellent for candied or sugared whole violets for garnishes to cakes. Just be warned that any moisture, including from your icing, can melt your sugared flowers. That means you want to add them to your moist dishes just before serving.
If you want to get fancy, which is absolutely recommended, color-changing drinks can be made with violet syrup by waiting to add the acidic component. For example, instead of making a shelf-stable syrup completely boiled down, leave your sugar/violet mixture thin enough to mix easily at room temperature, but be sure to store this in your fridge. Then, mix your cocktail in a completely clear glass using the syrup. Add your acid, lemon juice is the most commonly paired, just before drinking to watch the color change!
If you try this out, let us know! We want to know what you're up to.