Correlating each color, in its full intensity, to a percentage of gray on the value scale is often challenging. Often, it is a new concept for artists, especially beginning artists.
The above chart is not a perfect example of basic color value as it applies to a twelve hue color wheel, but it serves as an example of a valuable exercise in relating color hues to values. I highly recommend taking the time to create one. I also suggest that you use quality watercolor paper when doing this so that you don’t run into the same problems I did when laying down the washes.
The images on left and center are the chart in its first and second stage. The image on the right is the finished chart (the one shown in the middle) converted to grayscale in my computer. I will, in the near future, create the same chart in either acrylic or oil so as not to complicate matters with the issue of transparency and dilution of hue intensity.
Diamond color value charts: Watercolor media.