Occasionally there are white, or albino seeds, but the usual color is dark gray with black mottling. Chia seeds are used for ChiaPets because of their unusual seed coat which becomes mucilaginous when wetted. Mucilaginous simply means sticky. The mucilaginous seed coat enables the seeds to stick to the ceramic planter. The seed coat is mucilaginous due to a mucopolysaccharide.
Polysaccharides are carbohydrate polymers.
Starch and cellulose are more familiar carbohydrate polymers.