What does a little blue mean?

When you ask someone how they are feeling and they say "A little blue" they mean they are feeling a bit sad.

When you are mixing a green colour and your art teacher says add "a little blue" it means the colour is somewhat unbalanced in the direction of yellow and a small amount of blue pigment will correct the problem.

When you are asked about the roan you are riding, "a little blue" means your horse is a grey colour.