Here download a button, right click it and use your browsers 'save picture/image as' option. Specify a directory, and its done.
Now just add text and effects to suit.
These buttons are suitable for any background.

These are basic button shapes to play with. The buttons with curved edges are optimised for dark backgrounds. After downloading them, use your Colorise function to achieve the colour you want, then add text and effects in your paint package..