Clamshell mode brightness

Hi

I plugged in my new Macbook Air to a monitor for the first time yesterday.

I noticed that white pages, like this one, had a more orange hue than I expected. That didn't bother me so I just moved on.

But just now I closed the lid of my Air to try clamshell mode. The external screen instantly went to a brighter, bluer hue of white.

When I open the lid, swuitches back to more orangy.

What's happening? Can I change the settings to make it consistent.

(Apologies for my very technical terms: bluer, orangy etc.)