Click any of the color swatches available for options on the Schematic - Compiler page of the Preferences dialog.
Click the color swatch of the Grid Color field on the Schematic - Grids page of the Preferences dialog.
Double-click the color swatch on a PCB layer tab.
Click the color swatch of the Connection Color field in the Edit Net dialog when defining properties for a net loaded on the PCB. Alternatively, right-click on a net entry in the PCB panel (configured in Nets mode) and use the Change Net Color command from the context menu.
Color Chooser - this region of the dialog provides the controls for choosing the required new color. Three tabs are available, essentially giving you simple and advanced modes of color selection:
Basic - this tab provides a horizontal color list that you can scroll through and select the desired color.
Standard - this tab provides a hexagonal color selector filled with popular colors as well as controls for quickly choosing black, white, or various shades of grey.
Custom - this tab provides advanced controls for getting the exact shade of color required. Use the main color area to drag the cross hair to the general area of the desired color then use the vertical slider bar to the right to fine tune the shade. Use the Color model drop-down field to choose between two color models, either RGB (Red, Green, Blue) or HSL (Hue, Saturation, Luminance). The fields below update as you change the color controls above. Alternatively, enter the values for Red/Hue, Green/Sat and Blue/Lum directly.
Current - shows the color currently being used for the attribute.
New - shows the new color chosen for the attribute.
Custom Colors - this area allows you to store up to 16 custom colors, which is useful if you have finally reached a desired color through the color choosing controls and want to 'save' that color for reuse. Clicking on any of the custom color swatches will quickly assign its color as the new color.
Add to Custom - use this button to add the currently selected color to the custom colors palette.
Ensure the correct swatch to receive the color is selected on the custom color palette to prevent overwriting an existing custom color that you want to keep.