If you’re gonna do this, you’ll have to learn html and css. Get one of the dummies books and or take the free lessons on w3Schools.
To get you started, your form you should already have (why else be working on the background color if you don’t have a working form?) should be easy to wrap with a div like this:
<div class="myform">
<form>
<input>
<button>
</form>
</div>
Then you just style it by adding the appropriate css like this:
.myform { background-color: blue; border: 1px solid black;}