Here is what I use to make one of my favorite grays – and some other lovely neutral colors: Ultramarine (Green Shade), Jaune Brilliant No. 2, and Light Red. I am using Da Vinci and Holbein watercolor paints here, but you can use a different brand or a student grade paint or even a similar color combination from a Crayola watercolor set!
I like to have a little porcelain palette for mixing special color combinations like this. It keeps my main palette more organized and clean.
I’ve squeezed a tiny bit of each color into their own wells in my mini palette. Add water and transfer just a bit of the Ultramarine (blue) and Juane Brilliant (peachy-cream) into a new well. Playing with the pigment ratios I can create a whole new array of gray tones! (You can see just five variations to the left of the paper pictured below). If I want a darker, warmer option, I can do the same process with the Light Red (seen with the angular swatches to the right in the photo below).
This is a really fun exercise to try and see how many different colors you can make from just these two or three base paints. Once you become familiar with the types of neutral colors you can create, you can go back to that color for a painting. Just mix up a big batch in a fresh well!