Answer:
It doesn't live within a house, nor does it live without. Most will use it when they come in, and again when they go out.
When liquid splashes me, none seeps through. When I am moved a lot, liquid I spew. When I am hit, color I change. And color, I come in quite a range. What I cover is very complex, and I am very easy to flex.
You must keep this thing. Its loss will affect your brothers. For once yours is lost, it will soon be lost by others.
If you happen to wear one of these warm garments around, you might get doused in red paint.
By Moon or by Sun, I shall be found. Yet I am undone, if there's no light around.
Those with eyes bigger than their stomach will definitely leave the restaurant with one of them. It is named after a house pet as well.