I am a total rooky, and I mean rooky. Just made my first website, my first template and still needed a contactform.
My form was ready in just a few minutes. It automaticly adapts to the layout of my template, which is simply awesome. So why change background colours? Just make sure your template is okay.
About the size: At first I thought it was to good to be true, I made a beautifull responsive template but the form was the only thing that didn’t adapt its size. I send a mail to the developers and 30 min later I had a step by step reply how to fix it.
After fixing it (which took no more than 1 minute) I understood that I just overlooked some settings.
Guess that’s probably what you did.