Do Multi-Domains or Domain Mapping allow a site/content to be placed on the root folder?

Is Multi-Domain configured only to use subfolders or subdomains, or is it possible to place a WPM site on the root of the domain?

For example, my main WPMS is on http://www.rainbow.com
I have the following listed as domains in Multi-Domain
http://www.red.com
http://www.blue.com
http://www.green.com

It seems to me so far that if I already have hosting for red/blue/green etc .com then even with wildcards enabled I cannot even add those sites to the MultiDomain list without encountering an error on the Multi-Domains settings page telling me I have a Wild Card error, and when I try to add a site using that domain I get a 404 error "The requested URL /wp-admin/network/ was not found on this server." and the url in the browser address bar is http://www.red.com/wp-admin/network/

When I use domains which have no hosting whatsoever, I can add a * Wildcard A record and create a subdomain site, for example http://www.apples.green.com, but I can't get any content on http://www.green.com itself.

I have the Domain Mapping plugin installed, but when I try to map a site on the main domain, for example purple.rainbow.com onto http://www.purple.com, I can also only do so if that site has not hosting.

I have tried parking the sites on the main domain, but the errors are the same as with hosted sites.

All I want is to have WPMS on http://www.rainbow.com which has a dedicated IP address.
To be able to create subdomain or folder sites for http://www.red.com, http://www.blue.com etc
Have content available when visitors go to http://www.red.com, http://www.blue.com etc
And be able to offer subdomain or subfolder sites on http://www.red.com, http://www.blue.com etc for users.

It would be good if I could also use the email addresses on those domains and also include non Wordpress Multi-Site content on them if I wanted to.

If something needs changing at server level then I am sure my hosting company will oblige, but if what I am trying to achieve is actually impossible, then I'd rather know now.

Hope someone out there can help.