Putting food colouring into your cocktails (or mocktails) virtually guarantees that you'll have colour variation between batches. There's no guarantee you won't, in drinks without — but the odds that they'll be noticeable differences are much lower. It's also difficult to find a colouring agent that has absolutely no impact on your flavour or volume, given that they tend to be either gritty powders (that need to be dissolved in something before being added) or some consistency of liquid.
There are already plenty of liquors and liqueurs that are brightly-coloured, not to mention fruit juices and assorted other mixers — but if you don't know your colours yet, you might be best off just collecting a larger list than necessary, at the moment. Then, when you do have the colours, and are actually fully planning out the menu, you can match not only colours but also flavours.
Did you specifically want only non-alcoholic drinks, by the way?