How do I add custom colors to a protein sequence?
Select and Color Part of a Protein Sequence

Select the amino acids to be colored with a custom color.
Hover over the "Show Colors" button in the side toolbar, and choose Set Amino Acid Color.
Alternatively, click menu Edit → Set Amino Acid Color.

Choose the color, then click OK.
Switch Color Modes

If the "Show colors" option is not toggled on, a dialog will ask if you would like to display them. Click Yes to show the newly colored sequence.
View the Custom Sequence Colors

The "Shows Colors" button will be toggled on, and the custom sequence colors will be shown in Map and Sequence views.