Why The Colour Shift?

I was at the Fitzwilliam Museum here in Cambridge a few days ago and happened to look up. I may have looked up and seen the ceiling and the cupola before, but if I did then I don’t recall doing it.

I took two photographs within a few seconds of each other. I used the same camera for both shots. I had the camera in Manual mode. And because the scene was dark and I didn’t want to bump up the ISO, I took two shots with different shutter speeds. The first was 1/125th of a second. The second was at 1/15th of a second.

I knew that the shot at 1/125th of a second would produce and image that was too dark but I had the idea of opening it up in post processing or perhaps combining the two photos in post production by layering them in Photoshop.

Yes, I know – that was a very badly thought out idea. But I was sat on a bench and braced against a column, and that’s what I did.

So far so good.

I processed both images in Capture One 20 and here are the two photos.

Question:

Why is the cupola in the 1/15th second shot blue and in the 1/125th second shot it is gold?