Drivers: copy color

Hello,

I haven’t used drivers in animation very much, so I’m not always quite sure what to do. I’ve tried playing around with it and looking at a bit of the documentation, but I couldn’t quite get what I wanted:
Basically, I have a light (sun) in one layer and another sun in another layer, effecting that layer alone. While their intensity and atmospheric settings are different, I want the colors to be the same. Since the color of the first sun is being animated, I don’t want to have to keep copying the keyframes etc. I’m pretty sure there’s a way to ‘copy’ the color of the first sun to the other with drivers, though if there’s another way to do it it would also be nice.

EDIT: I also want to be able to have the color of a third sun be connected to the color of the horizon. I’d assume the function to do so would be similar (yes, the horizon is also being animated in color different to the first, main sun)

Thanks for any replies!