What you are looking at is called an accessory kerf. It's purpose is allow Marvin to mull or join windows. A mull clip snaps into that kerf cleaning up the mull. There is a piece available as an option that will fill that "tunnel" on all four sides.
As for the weatherstrip, there are three color options: black, beige, or white. Not sure why they chose black on a white window.

The Marvin quoting system defaults to black weatherstrip so if you wish to have them with a different color you need to make certain that this is changed. At least that was the way it was back when I was selling them but they may have changed the system.

I wonder if I am working with someone who doesn't know their stuff.....I told them I didn't like that opening around the window and they never mentioned anything so I called Marvin and they said that is the way it is. Nothing I can do about it. Hmmmm, think I will have to call again. They also told me the weatherstripping only comes in black.

As I said earlier, you can't order a window without the kerf but you can get a piece that covers it (part# A1538). Reference that part number when you next discuss this with someone.
And the Marvin quote system (OMS)defaults to white weather strip when you choose white cladding but you can also choose beige or black if wanted.
I would recommend that you talk to someone else with more experience or contact your local distributor. Go to marvin.com and check the dealer locator to see if you have a Design Gallery nearby. These dealers sell only Marvin.

Ah thanks for the heads up eastbay been a few years, lol.

ok, I think we might be talking about 2 different things. See picture. As you can see the window in the picuture has wood around the frame except for where the lock is, in the Marvin it is open. I called again and they said that is just the way it is.

I never have had dirt in those gaps as an issue on my Marvin Casements. If you do your window is not sealing up. My father in law has that problem in his Pella windows but that is the least of his concerns since they rotting out and bowed.