How to chage "Submit" text?

How do I change the text on the submit button?

You can follow the instructions here to change the text of the submit button:
http://jetpack.me/support/contact-form/#customize-submit

Also how to change the color?

You can customize the look of the button, as well as the look of all other elements on your site, thanks to CSS. You can add custom CSS to your theme stylesheet, or to your custom CSS editor available under Appearance > Edit CSS in your dashboard.

You can target Jetpack’s Contact Form submit button with the following selector:

.contact-form input[type="submit"]

If you’re not familiar with CSS, I can give you the exact code to use if you let me know your site URL, as well as the changes you want to make to the button.

I hope this helps.