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To get any blocks that you want to be viewed by anonymous users, the settings is in admin groups. click on edit anonymous user and check the blocks that you want the users to view.
The colors, some are CSS in origin, and some are in the theme.html. Check both to find the setting that you wish to change.
To upload a theme, just unzip the theme on your computer then ftp the unzipped folder to the theme directory. Be careful though, when you unzip usually there is extra folders, just go down to the last full containing folder, and that is what you want to upload. Same with modules, but of course you would upload them to the modules directory.
Make sure that you check the documentation section on this site. Lots of good information for starting out with Xoops.
BTW welcome to Xoops.