How To Store Colors In Variables For Quick Change in Whole Theme?

Hi

Many times our clients like everything but not the color theme or color palette or maybe a single color, and we have to give them multiple options. I always have to group similar colored objects and then apply a Color Overlay so that if i have to provide multiple options i can achieve that.

To Better explain say i have 3 Circles And 3 Squares.
In Theme 1 , i want the circles to be red and squares to be green.

In Theme 2 , i want the circles to be Blue and squares to be Black.
and so on

To achieve this i have to Group All Circles And Group All Squares and apply a Color Overlay.

I Wanted to Achieve it in a Different Manner

Say i Define Two Colors
Color A: Red
Color B: Green

Then when i am drawing circles i define their Color to be Color A, Similarly Squares to be Color B

Now if i want to change colors i just need to change my Color A & B Values

Of-course in my example it looks easy to Group and Do a Color Overlay but in a Full Design, this is not just possible there are texts, objects, shapes, and more. Was just wondering if this is possible and if not then why not?