Change background color of Search Box widget

I want to change the color of background of the Search function widget I put in my narror/left sidebar.
I want to change it to this:
#764CA1
to match my blogs theme.

There is a problem thought, my theme also has a Search function up in the header.
I would not want that color to change becuase purple and black would not fit the color scheme of my blog.

(I can look and see if there is a way to disable the theme Search function in the header)

The page I need help with: [log in to see the link]