Hey there,
Thanks for posting. The plugin settings don't provide those options directly unfortunately, but your desires are both things that can be accomplished by adding your own CSS code.
For changing the background color of your input fields, you should be able to set that by adding some CSS code to your Wordpress theme's stylesheet. To identify the element that needs to be targeted, you can use a tool like Firebug or 'inspect element' in your browser. This code should allow you to change your input field's background color:
#mc_signup_form .mc_input {
background-color: red;
}Where red can be any hex value you'd like. For the form fields to be aligned, that really depends on the type of layout that you're going for. I'd recommend using my suggestions above (Firebug and inspect element tool) to identify the elements that need to be targeted, then doing a bit of research to find the best techniques in aligning form fields the way you want. To help you get started, I found a stack overflow article that may be helpful for the type of customization you're looking to do:
http://stackoverflow.com/questions/10868640/align-html-input-fields-by
Best of luck!