vertical image & color left and right of page

i currently have a lot of white space on my blog. i would like to add a little color to the exterior of the blog vertically. the color will appear near the edge of the screen almost like a frame for the page. I believe i need to use repeat, but cannot figure out how.

i’ve seen this done on many sites and blogs, but cannot figure out how to change the css to reflect this.

i appreciate the help. site address: https://www.portorangeproperty.com