Revit Colours Window Help

[rpe_ryd]

Seems very basic but i've never understood this, can anyone help explain to me how I add colours to the colour blocks that i've highlighted in green in the attached screenshot please? I've only ever been able to use the very first block that i've circled in red. A quick explanation or link to a tutorial on it would be appreciated, thank you.

[rxi.gg · Accepted solution]

select a blank space, then select the color you want, then Add

[rpe_ryd]

Thank you, I wasn't selecting a blank space first so everytime I was adding it was just replacing the first block. How simple!