A water soluble colour is suitable, as long as you also add a UV filter to your formula.
These are generally easy to find here in Australia from places such as New Directions (I'm not sure where you're situated).
Easiest way for small production, dip a paperclip into the colour, and dip into your fragrance, stir. Repeat for more colour.
The UV Filter, depending on the type (it's essentially the same additive as a sunscreen, such as Benzophenone (2,3,4,5)). This should sit at around 0.50% of the final product, but in most countries can sit at a max of 5-10%...although not entirely required.
This will keep your colour stable.