You will have to edit the “bg-repeat.jpg” file in the images folder. But remember, this pattern is applied to all the pages in the theme, so editing this file will affect the body as well (not just the header). You will have to use Photoshop to edit this image file.
Most of the color styling are available in the default.css file. You might want to look into this forum post as well https://www.livemeshthemes.com/support/forums/topic/how-to-change-the-orange-color-of-the-theme/
To know about all the available features of the theme, I would recommend you to go through the documentation of the theme and also load the sample data.
Regarding the segment id, if you want to target a particular segment, you will use the id else if you want to target multiple segments then you might want to use the class. Here is a post on that http://css-tricks.com/the-difference-between-id-and-class/
Regarding the footer, Pls reply as a private message here with the site URL and a temporary login to the WordPress dashboard and I can fix it.