Very subtle, I don't know if the rainbow is strong enough to make it the focus of the picture. I look at the clouds more. Maybe if you did some editing work in Photoshop, you could really emphasize the rainbow. Just a suggestion.
I have to agree it could do with a little work in Photoshop, because it looks a little grainy...the frame should be a little thinner maybe so that it doesn't distract the attention away from the photo. But all in all, not to bad, i like the gloomy clouds contrasted with the pretty rainbow! Well done...must have been some rather bad weather...