To the right of the Build It tab, use the Design It tab to choose the colors,styles, and fonts for the form or response email you've selected. It's important to be aware that style changes are made universally and not form by form. When you edit or make a change to any element of the form we apply the same change to each of the other forms and response emails for your list.

You can also use the Auto-Design button at the top of the page to fetch colors, fonts, and images from your website automagically. Visit MailChimp's Knowledge Base for more tips on customizing the look and feel of your list forms and response emails.