Spices are strongly flavored and/or strongly aromatic parts of plants, which are used in small quantities in food for color, flavoring, stimulating odor or as a preservative in cooking. They are also used in cosmetics for color, fragrance and their therapeutic properties.
Alkanet is a perennial that has a bright blue flower. Botanically know as Alkanna tinctoria, it is its' thick, red-maroon taproot that is sought for use as an additive, and is usually used as a powder. This root releases a rich, dark red dye when it is infused in alcohol or oil, and a less intense shade of red when it is in boiling water. Alkanet root is used as an astringent, and for its antimicrobial and wound healing properties.
In soapmaking alkanet root is often used as a colorant because it offers colors ranging from gray-lavender to deep purple, and from a pastel blue to a dark blue, all depending upon the alkalinity of the soap.
Black Walnut hulls are crushed and powdered, and frequently used as an additive for soap. Their powder contains vitamin C, zinc and a naturally occurring chemical that has antibacterial, antiviral, antiparasitic, and antifungal properties. Herbalists will frequently use black walnut hulls to treat a variety of skin issues. In soap, they will provide a lovely nut-brown color, but are also good for treating eczema and acne. For coloring your cp soap, just add the powder directly into your soap pot at trace and mix it well. For melt & pour soap, blend it in a small amount of [heated] glycerin in order to release the coloring, then strain it and add it back into the melted base drop by drop, until you get the color you want.
Remember that with most herbs you can either add them directly into your soap pot at trace, or you can infuse them into your oils, strain, then add the colored oil into your soap pot as part of the base.