List the skin colour of the superheroes with 100 attribute value.
skin colour refers to colour.colour where skin_colour_id = colour.id; 100 attribute value refers to attribute_value = 100;
SELECT DISTINCT T2.colour FROM superhero AS T1 INNER JOIN colour AS T2 ON T1.skin_colour_id = T2.id INNER JOIN hero_attribute AS T3 ON T1.id = T3.hero_id WHERE T3.attribute_value = 100