Water drops aren't the 'color of water', rather being transparent they're the color of whatever surface they're lying on. So if the leaf it's lying on is green, then the water looks green.
The highlight on the top of the drop will be white. The shadows are darker tones of the green. The refracted light at the bottom of the drop is a lighter tone of green. If the drop were on a red leaf, then the water drop would be in tones of red. The three drops above show this clearly.
Tips for painting water drops:
- If you're working in watercolor, use masking fluid to preserve the highlight (reflected light in the drop) rather than trying to paint around it.
- Until you're confident about your drops, sketch a drop first in pencil on a piece of paper before you paint it; if you've got the highlights and shadows correct, it'll look realistic.
