Orkney Image Library

Two things are well demonstrated in this nice pic: the 'reversed' spectrum in the outer bow, and the marked difference in brightness and colour saturation between the area within the inner bow and the rest.
Although it's been commented on once or twice, I don't think we've seen a really satisfactory explanation for the latter phenomenon on this site to date. (Please correct me if I'm wrong.)

I came across an explanation for the light area below a rainbow ,which is:
The light paths for parallel rays through a water droplet which produce the primary rainbow comes from the highest drops which have single reflections. All others reach the eye from lower drops, lightening the sky.

I'm afraid that's gobbledegook to me Neil.

Me too Ian, and it came from a scientific source.What do they say about scientists, something about eggheads.....?

In desperation I turned to the fount of all knowledge, Wikipedia, and here is their explanation:
. . . each raindrop is a sphere and it scatters light in a many-layered stack of colored discs over an entire circular disc in the sky, but only the edge of the disc, which is colored, is what is called a rainbow.
Clearly fearing that this hasn't quite got the message across, Wikipedia then quotes an expert:
"Each colour [a momentary lapse into English spelling] has a slightly different-sized disc and since they overlap except for the edge, the overlapping colors give white, which brightens the sky on the inside of the circle. On the edge, however, the different-sized colored discs don't overlap and display their respective colors - a rainbow arc."
Seemples.

Admirable but I'm afraid still gobbledegook Ian. How say you?

I always think of light in terms of stacks of coloured discs, don't you Neil? And when it comes to circular discs (as distinct from, say, square or oblong discs) in the sky, the talk in Stromness is of little else when rainbows are about.
Yes, gobbledegook on stilts.