How to change default button colors?

Hi,
My website is nearly finished and this could be my last request for a while…at least I hope so 🙂

If you go to http://www.oakbrookallstars.com/contact/, you will see that submit message button in a contact form has a default value of orange color. I would like to change it to green #50a862 color so it does follow the overall color scheme of my website.

The same applies to Subscribe button when hovering over the button. This button is located in the footer 4 area “Sign up for our newsletter!” I would change only the hover effect on this button.

How do I change those 2 buttons to #50a862 without messing up with other CSS code?

Attached are screenshots.

Thanks in advance,
Mika