Well, possessive endings change for en words, ett words, or plural. It looks like color works the same way. En words would be vit, ett words vitt, and plurals (in this case, the cats) would be vita?
No the är is in there, it just blends with katterna when you speak quickly.
I heard it as "katten är vita". Is this how spoken swedish really sounds? I only knew from the grammar that what I heard doesn't make sense. The slow playback revealed that the first word is katterna.