What is the most frequent product category code of the products?
select product_category_code from products group by product_category_code order by count(*) desc limit 1
What about the color description instead?
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(*) desc limit 1
Give the least frequent now.
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(*) asc limit 1