CREATE TABLE ref_colors (color_code TEXT, color_description TEXT)
CREATE TABLE product_characteristics (product_id DECIMAL, characteristic_id DECIMAL, product_characteristic_value TEXT)
CREATE TABLE characteristics (characteristic_id DECIMAL, characteristic_type_code TEXT, characteristic_data_type TEXT, characteristic_name TEXT, other_characteristic_details TEXT)
CREATE TABLE ref_product_categories (product_category_code TEXT, product_category_description TEXT, unit_of_measure TEXT)
CREATE TABLE products (product_id DECIMAL, color_code TEXT, product_category_code TEXT, product_name TEXT, typical_buying_price TEXT, typical_selling_price TEXT, product_description TEXT, other_product_details TEXT)
CREATE TABLE ref_characteristic_types (characteristic_type_code TEXT, characteristic_type_description TEXT)

Give the color description that is least common across products.
SELECT t2.color_description FROM products AS t1 JOIN ref_colors AS t2 ON t1.color_code = t2.color_code GROUP BY t2.color_description ORDER BY COUNT(*) LIMIT 1
SELECT "t2"."color_description" FROM "products" AS "t1" JOIN "ref_colors" AS "t2" ON "t1"."color_code" = "t2"."color_code" GROUP BY "t2"."color_description" ORDER BY COUNT(*) NULLS FIRST LIMIT 1