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

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" "t1" JOIN "ref_colors" "t2" ON "t1"."color_code" = "t2"."color_code" GROUP BY "t2"."color_description" ORDER BY COUNT(*) FETCH FIRST 1 ROWS ONLY