How to Set Custom Color in Session Manager

Maybe i am missing something obvious but i would like to use a custom color. There is a custom color option in the dropdown for background color, advanced tab, session manager but it is set at #F0F0F0. how do i change this or even better, add more custom colors?

There's an "individual" item with a color picker in the dropdown.

Thanks. Missed the Custom at the top of the dropdown. Not enough coffee???