I’m not a master colorist by any means, however I dabbled in water color painting long enough to know that if there’s a color you’re interested in, you buy it (or at least the closest thing to it). There are several good reasons for that. Expediency is one. Consistency is another, since you never know whether you might need another batch of the same color. How many drops of blue was that again? You follow me. Also, sometimes it’s not easy to predict what the result of a color mixture might be. You might have labored hard to get just the shade of purple you want, and then that one drop of orange…argh!
Myself, I try never to mix more than two colors, and then only when I really must. For example, I had a green apple in mind this week, but the green I’d bought was a little too blue-heavy, a bit too much like an evergreen tree. A drop of bright yellow and I got the shade I was after, but I wouldn’t have pressed on from there to make aquamarine. Keeping your colors bright usually means not heaping up too much pigment in any one batch, so as to let the manufacturer’s color shine as brightly as it can. Bottles of gel colors only cost about three bucks. You’ll find it’s worth it.