Civilization IV: Colonization is a separate game from Civilization IV and it's Expansions, Warlords and Beyond the Sword?

So you don't need Civ IV or any of it's expansions to play this, and in turn this game doesn't add anything or update Civ IV, because it's not a expansion.

I'm a little confused because it's listed under Civilization IV but the overview seems to indicate none of the other Civ IV games including Civ IV are necessary to play it. What's the deal?

Yes.

It's an independent game that is being marketed under the label of Civilization IV and from it's core uses mostly Civilization IVs engine but there are some differences (like in graphics) making it incompatible directly to Civilization IV.

Civilization IV: Colonization is a separate game from Civilization IV and it's Expansions, Warlords and Beyond the Sword?

Right.

So you don't need Civ IV or any of it's expansions to play this, and in turn this game doesn't add anything or update Civ IV, because it's not a expansion.

No, all you need to play Civ IV: Colonization is Civ IV: Colonization.

I'm a little confused because it's listed under Civilization IV but the overview seems to indicate none of the other Civ IV games including Civ IV are necessary to play it. What's the deal?

The game has Civ IV attached to it for marketing purposes. Also because the game uses an updated version of the Civ4 engine. The whole game is essentially a gigantic reworking of standard civ.

Yes, it is very confusing that they listed it in the Civilization IV section, but it's easier than adding a whole new sidebar category.