Most of the time, you use sliders to change colors.
However, when using the Adjustment Brush and the Split Toning panel, you may need to choose a particular color.
Click the Color box . . .
. . . and the Select a Color window appears.
Think of the window as being like a graph.
The x axis, the horizontal axis, is the hue.
As you click from left-to-right, the hue changes.
The values go from 0 to 359.
Saturation is on the y axis, the vertical axis.
A hue is more saturated at the top, and less saturated further down.
The values go from 100% (most saturation) to 0% (least saturation).
Click on the chart.
The hue/saturation combination that you clicked on appears in the upper-right corner of the window.
You can click on the tiny white square, hold, and drag.
Or, use the arrow keys on your keyboard to move the square.
You can use the two tools at the bottom of the window to change the hue and the saturation.
To change the hue:
1) Place the cursor on the value to the right of the H.
2) Click, hold, and drag left-and-right.
Saturation has a slider.
You can choose a color from elsewhere on your screen.
Do the following.
1) Click inside the window, and hold.
2) Move the cursor to the color that you would like to select.
3) Release the mouse button.
Click the x to close the window.