How do you change colours/backgrounds of forms?

We are currently creating our first contact form and one question we have, is how can we change the background colours of the form? We have a brand template which pulls through a logo but want to change the background colours of the form so it’s in line with our brand colours. How can this be achieved? 

In email remplates we can update the hex codes for backgrounds and font but I can’t find a way to do this in forms. 

Also we have an out of hours banner appearing at the top of the form and I don’t know how to switch this off. How do you decative a banner appearing at the top of the form?