I found the code for how to add a gradient to your WordPress Site background in reference to the Twenty Eleven theme, but changed the color to blue (see below wherever #5586CD is listed). I used this in the Executive Pro Genesis Child Theme and place it in a custom CSS file (via Jetpack). Here is the original post and thank you to Scott!
If you want to change the color, put in your hex code wherever #5586CD appears. The gradient will go from that color to white. If you want to use a different color besides white, change everywhere that you see #ffffff below.
background: -moz-linear-gradient(top,#5586CD 0%,#ffffff 100%) fixed;
background: -webkit-gradient(linear,left top,left bottom,color-stop(0%,#5586CD),color-stop(100%,#ffffff)) fixed;
background: -webkit-linear-gradient(top,#5586CD 0%,#ffffff 100%) fixed;
background: -o-linear-gradient(top,#5586CD 0%,#ffffff 100%) fixed;
background: -ms-linear-gradient(top,#5586CD 0%,#ffffff 100%) fixed;
background: linear-gradient(to bottom,#5586CD 0%,#ffffff 100%) fixed;
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