Guys-sorry it took so long. I meant to do this after I made the change.
The plugin uses a full color button and a greyed out button. So to get these, I went to PayPal, copied the Donate button with the credit cards (which was the one I wanted to use), copying it by right-clicking and “save image as” to my hard drive. Then I duplicated it, opened the copy in Photoshop, and desaturated the image (hue/saturation or command/control-u) by moving the saturation slider all the way left.
Then I used my FTP client (Fetch) to load the two images to site/wp-content/plugins/seamless-donations/images/
Then, using my FTP client, I went to the seamless-donations plugin folder, and opened the file named dgx-donate-paypalstd.php using TextWrangler (use the editor of your choice). I scrolled to lines 275 and 276 and exchanged the names of the new files for the old names.
REMEMBER THIS (and/or copy these instructions to your drive) SO IF THE PLUGIN GETS UPDATED YOU CAN REPEAT THE PROCESS.
And you’re done!