procedural color replacement/ swatch matching?

after searching forums, asking google, and even breaking out my Dummies book all weekend I'm breaking down and asking the community.

I am trying to find a way to quickly match the colors in a given image to a custom swatch set, and vice versa.

I use photoshop to mock up murals and multi layer stencils. I have the product line of paints I use loaded into a custom swatch. I want to be able to take a given image, convert it to this color palette as close as possible. yes, you can do color replacer, but im wondering if there is a more efficient way of doing things as my palette is close to 50 colors, and that gets tedious fast.
maybe I'm not asking google the right question? is the answer 42?

best,
Babel