I was hoping to get some help with a calculated field in a pivot table.

I'm trying to create a "% of sales" formula (value of each color/total).
I'm navigating to (pivot table\formula\calculated field) to build the
formula, I'm lacking the knowledge to use the field items to build the
formula.

Any help would be greatly appreciated.

Color Unit Sales
Black 10
Brown 10
Red 10
Total 30