slider.php controls featured slider. The javascript controlling this is located in the footer.php file.

Any styles are controlled in the style.css file under this section:
11. FEATURED SLIDER

ok. I found the image for this in the images/slider folder. I'm not good with photoshop. What would be the best way to change the green color? I would like orange, but maybe would like to change it to a different color later.

Photoshop would be the easiest. You could try using CSS3 to create the buttons instead of you want:
http://css3generator.com

If you need to, you can always hire a developer for any customizations. We can't help with that other than to point you in the right direction.

Thanks for the link. I'll try that.

And is it possible to disable the homepage slider ?

The slider will automatically turn into a static image if only one slide exacts. The controls will disappear automatically. If you don't want a slider you can use a regular page template OR delete the slider.php include in the homepage.php file.