Planning

1. Decide on the placement of the belt relative to the dress and where you'll position the belt snaps. In this project, I'm using the smaller snaps for the belt. Lastly, trace the lines between the belt connections and the petticoat connections to ensure separation of the lines.
2. Remove some of the jewels on the belt to make room for the color sensor. 

Sewing

Sew in the color sensor with some regular black thread to keep it in place. Sew conductive thread from the 4 pins on the color sensor to the placement of the belt snaps. The belt is pretty narrow so make sure to space out correctly. A banana type shape for the snaps will probably work best.

Use a scrap piece of black satin and sew it on both sides of the belt sash to both cover the stiches and keep them from touching each other.

Instead of just tying the belt on, you can create a bow at the back at the right length and use non-conductive snaps to put it together. You can also add a few non-conductive snaps around the dress to keep the belt in place.