Dougal and the Blue Cat - The Magic Roundabout Movie (1980)
This is a rip of the 1989 UK VHS release. It is the English Language dub and not the original French version.
From IMDb: Life at the Magic Roundabout is disrupted when a blue cat called Buxton
finds his way into town. Everyone loves Buxton except for Dougal, who
discovers the cat's mad plan to become the king of blue army and destroy
all who are not blue.