Although the bicycle components are usually made so that their weight is lower as possible, you can add a nice coloured grip to your shifter in a few easy steps.
Step 1: The Sugru
Clean the shifter with alcohol, so that Sugru will adhere better.
Now you need a pack of Sugru, you can choose the colour you like more. Cut the packet along three edges, cut the Sugru in two equal parts and begin blending it, so to remove any air bubble and imperfection.
Step 2: Place Grip
Now you can stick half material on the shifter side. Just shape the Sugru with right dimensions, then push it on the clean metal. Do the same for the next side.
Step 3: Round It
With your fingers tap the Sugru so that it will take a round shape, and it will make contact with the leverage edge.
Step 4: Add a Texture
When you're satisfied with the grip shape you can choose a nice texture to apply on it as a bas-relief.
I used a piece of cloth, but you can use everything, from a screw head to knife blade. Maybe you can use a small fraction of the Sugru package to make some test. If you make a mistake you can flat the Sugru surface with your fingers and apply the texture again. You have about 20 minutes or half an hour to complete the molding, then you have to let the Sugru rest for some hours.
Now changing gears will be a real delight!