Both the text and colour of the “Sign Now” submit button can be changed to suit your site.
Change the text in dashboard > SpeakOut! > settings > Petition Form tab > Submit button text
If you want to make substantial changes to the styling of the petition form, you are probably best to use a custom CSS style sheet – read this
If you would just like to change the colour, use your theme’s custom CSS feature and add the following, modifying the colours to suit:
.dk-speakout-submit {
background: linear-gradient(#ff9a40, #d94200);
border: 1px solid #d94200;
box-shadow: inset 0 1px 0 0 rgba(255, 255, 255, 0.5), 0 1px 4px rgba(0, 0, 0, 0.4);
}
If your theme doesn’t show Additional CSS you can access it directly from yoursite.com/wp-admin/customize.php