Do I have to use IMCE?
No. Acquia Cohesion allows the site builder to select, either use of IMCE or Entity browser for browsing and selecting images.
Acquia Cohesion renames to Site Studio from version 6.2. Tell me more.
If you're removing styling from a base style, those styles still apply until you have saved the base style.
Base styles are CSS styles for HTML elements.
Color tags allow you to create groupings of colors based off of the color tags that you define in the website settings color palette.
Yes, this is possible by creating a custom element.