There are three different colour Jewels that only appear in Rayman 3: Hoodlum Havoc' each giving different amount of points. They can be found anywhere or, once you have destoyed a cage and some Teensies come out, they may give you some.
The most common jewel, it gives Rayman 10 points once he has collected it. Their appearance is shaped like a diamond with a point on the top.
This jewel gives Rayman 30 points when he has collected it. Their appearance is exactly of a ruby.
The green jewel is the most rare, and there is only a few in the whole game. But they give Rayman 1500 points, much more than the other jewels.