[chimpansteve]

I don't know how it works in the US (and tbf, I'm not much wiser after reading this article), but the UK it falls under trade dressing - eg the Royal Mail have rights to use one shade of red on postboxes and delivery vans, and if you're setting up a rival delivery company you can't use "Royal Mail red". There's nothing stopping anyone in an unrelated field using it though.

[bdowling]

It's the same in the U.S. A trademark is always tied to specific goods and/or services. In general, someone else can use the same name/color/design/whatever for unrelated goods or services so long as the way it's used doesn't cause a "likelihood of confusion" to consumers.