You will need:
Three ring sections laser cut from 3mm thick acrylic sheet of the desired colours (see the next step for the design and sizing). I usually order from Formulor, the German Ponoko partner;
Glue for acrylic parts. I used Acryfix 1R 0192
from Evonik. It gives a good strong bond. Work in well ventilated conditions;
Waterproof sanding paper grit 320 and 1000 (800 probably works too);
Polishing compound for plastics or paint (I used a “renovating” compound for tarnished car paint, which combines a wax with some very fine polishing grit);
A soft cloth or a polishing wheel;
Some non-stick (baking) paper.
Use a plastic basin to work in with the wet sanding paper and the polishing compound.
A calliper comes in handy to take the correct size of an existing ring.