When something is either muted and drab or incredibly boring, it has the quality of dullness. If you want to counteract your bedroom's dullness, why don't you paint the walls bright yellow with purple polka dots?
The dullness of late winter gradually ends when spring finally arrives with its bright colors and shining sunlight. The dullness of your most boring class will eventually come to an end as well, when the bell rings and it's time for lunch. Dullness describes a lack of vividness or excitement, and it can also be used for a lack of intelligence: "My dog is sweet, but her dullness makes it impossible to teach her any tricks."