Find the css file for your template (it's usually in the theme's folder somewhere - yoursitename.com/wp-content/themes/yourtheme/), open it and search for string '#sidebar' . There should be a row like 'background-color: #018294' or 'background: #...' . The value after the '#'symbol is the color. Change it to whatever color you want to try and save the file.
it's simple, just add these codes to your CSS file: ( you need to create a div called sidebar) #sidebar { background: #fff; (use your own color code) } remember one rule please, backup first and replace.
why you used h3 ? I want a background color for whole sidebar column - something like shoemoney.com or johnchow.com
Post edited, i added h3 by mistake try this now and it should work, if not PM me the download link of theme, I will fix this Thanks!