Is there a CSS to change background colour of a matrix?

Hi,

To change the background color of a matrix field, you can add this code to your form:

http://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes

.form-matrix-values {
    background-color : #6DD0F2;
}

This would result in a blue background for the matrix field.  Here is a quick test form to show you how it looks:

https://form.jotform.com/53284919435969

If you have any further questions, let us know and we will be happy to help.