I went to an interview a very long time ago, at an interior designer's, where I was asked "what are your favourite colours?" Having been shown around and seen the work they were doing there, all in pastel shades, I replied "pastels, pale colours, mainly". I was wearing a long black skirt, black top, midnight blue jacket (with leg of mutton sleeves - it was a very long time ago!) and knee high black suede lace up boots. I didn't get the job. The stupid thing was while I was answering I was actually thinking to myself I don't have a favourite colour; I enjoy whatever colours are right, whatever works, what looks good in its context. I like good colour combinations.
I think that's a much better answer, and it still bothers me that I didn't give it. My daughter is at the age where she thinks it's important to know what your favourite colour is, and it bothers her that I don't shut up when she asks me, because I'm listing all the colours I've got in my head at the moment that feel good together. Daddy likes purple. That'll do.
One of the best things about decorating cookies is when I have free rein to choose my colours, and one of the most frustrating is when I have to copy them, usually for a character set. I can't 'tweak' the colours so they sit nicely together and feel good in my head, because they won't look like they're 'supposed' to.
I try to mix colours in an order so I can reuse the bowls and spatulas, so I'll mix ivory, take out what I need, make the rest yellow, take out some to keep for yellow, make orange with some and green with the rest. This often seems to work to keep the colours together, but I hadn't thought about why until I read LilaLoa writing about HUE. She mixes a little of each colour into the rest, and it brings the set together perfectly.
Sometimes though it's nice to go for just one really bold, stand-alone colour. I have a friend who was told it's not possible to make red royal icing, so here's a bag just for her.