If you edit your style.css, you can remove this code from line 3141 – .epik-darkblue input[type="submit"]
Then add it on its own line which will separate it from the other code. You can add it on its own line like so –
.epik-darkblue input[type="submit"] {
background: #d91420l;
}
You can change the color to whatever you want and it should change that button instantly.