WordPress keeps the content (words and pictures) separate from the design of your website. This means it is very easy to select a different design for your site.
At the moment however the design options for NorfolkParishes are limited to a choice of green, blue or red, or to go with the standard WordPress format. Over time more designs might be available but for now it is a choice of three.
Different designs are known as Themes. The Norfolk Parishes theme is called Norfolk Parish Councils Theme. It is one theme that comes with three colour options.
How to change the colour of your site