New ad units automatically get assigned the "Unknown" category. Specific categories for ad units of the "Site" type are assigned by our moderators normally within 24 hours after you embedded an ad unit on your site and started generating unique traffic.
To change ad unit colors you may append GET parameters. Inspect the following URL as an example. Also you can generate this code via the web interface at the ad unit's page.
Is it possible to insert multiple ads on the same pages with different sizes? Can I submit the same website twice?
Yes, you can create as many ad units for a single page as you want, but it doesn't mean you will earn more. Please read this article for details.
Should the "Anonymous" type be used for dynamic pages with no set URL?
The “Anonymous” type is used for the traffic sources that can’t be verified by the A-Ads bot (e.g. mobile applications, browser extensions, etc). You can use it for dynamic pages as well, but you are more likely to earn more if you set the "Website" type since many advertisers don't pay for unidentified traffic.