Colored resin jewelry can be made in a wide variety of colors and shapes.
Opaque pigments are available for adding in small amounts to resin, which will produce a solid color. Transparent resin can be tinted with a small amount of dye.
Resin manufacturers produce liquid pigments for use in their own products. These pigments can be mixed to produce various color hues.
These pigments are very concentrated; you should only use very small amounts otherwise the resin will not cure and will remain soft and flexible.
Powdered pigments can be obtained from art suppliers and can be used to color resins.