Key graphics are drawn from the stock Android open-source keyboard.

Unpressed key background: btn_keyboard_key_normal_holo_light
Pressed key background:   btn_keyboard_key_pressed_klp_light
Shift "on" indicator: btn_keyboard_key_normal_on_ics_dark
Shift "off" indicator: btn_keyboard_key_pressed_off_klp_dark
Whole keyboard background: keyboard_background_holo

Many of these stock images are semi-transparent, and contain a translucent glow or shadow around the on/off indicator. To pull that translucent outline from the original image and copy it onta  enw one, I used the Gimp "set color to alpha" tool. The general technique is this:

1. Open the original image with the shift indicator in Gimp.
2. In a layer below it, create a layer filled with the color from keyboard_background_holo
3. Merge the two layers together (so the combined image is no longer transparent)
4. Select and cut out the central, opaque part of the indicator.
5. Now, you'll have the key itself, which is mostly a solid background color, and a bit of it will have the translucent glow/shadow on it.
6. Use the color picker to pick the color of the solid background of the key.
7. Now use the Select By Color tool to delete all of the solid colored part of the key
8. Now you have an image of just the background glow, and you have the key's solid color picked as your foreground color.
9. Do "Colors -> Color to Alpha...". This will turn the opaque background glow into a transparency, essentially pulling out the tint that had been placed over the original background color of the key.
10. Now you can paste this transparent glow onto a new background color and it will tint it correctly.