One of the “holy grails” in prosthetics is laminating an awesome looking straight carbon fiber socket. Many resins have a yellowish tint to them, even if it looks awesome at first, it may yellow or gray over time. If you add black pigment to your resin before mixing in your catalyst you will have a jet black socket once everything sets up.
Another tip is to use a scale for mixing resin, pigment, and catalyst if you are not already using one. Putting in the correct amount of catalyst will give you the best result.