Annatto seeds come from the Achiote tree, which is native to South America. It is used in cooking to impart yellow color and also in makeup. The Achiote tree is also known as the "lipstick tree"! Annatto powder is ground annatto seeds.
Annatto yields a yellow to orange color depending on the method of infusion and the amount used. Recommended usage is 1/2 teaspoon of powder per pound of soap. You can add it directly to your soap batch.
You can also infuse your oils by putting the powder in a coffee filter tied into a little bag and doing either a hot or cold infusion. Replace the infused oil for the same oil in your soap recipe. For example, replace olive oil with infused olive oil. You don't want all of your oils to be infused as the color will be very deep and will tint your lather. Have fun experimenting with the wide range of colors you can get from this seed!