Good Question Kragskov,
The answer is that it depends on what part of the template you are trying to change the color scheme in. If the color is inside of an image then the answer is no. All images are property of Auctiva and in order for those images to be manipulated we would have to do this. You may fill in a suggestion form at this LINK and we can look into this. If it is a background color that you want to change you can look into the html code find the color you want to change and replace it with one of your own liking.
To answer your other question about creating a new section for warranty and return info the answer is yes. The best way is to save your template the way you would like then when you go to use it in your listing you can simply type that info into the description area on the lister page.