how can i change colour of submit button

Just click on the submit button the choose button style. You will have a variety of colours and style there.

You can also inject this CSS to change the background color:

.form-submit-button{
background: red;
}

Here's how to inject custom CSS https://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes.