For the most part. It is not something usually set in stone, however, and some clans may have the same colour.

[Mitsuhide's eyes slide closed, for a moment.]

Lord Motochika is ruler of an island, and very much a man of the sea. To be far from it for too long unsettles him, I think, though I... I now know he would give it up, for the right reason. That close association with water, and the usual associations of the colour blue with water too, are why it makes me think of him.