to wonder why the expensive concealor that looked great in the shop...

[ladymontdore]

...when I tried it on yesterday, today has highlighted my spots in the manner of an orange highlighter!

Is it the light?
Have I faded overnight?
Am I such an unskilled makeup artiste?

It's probably oxidising or reacting with your skincare. A decent brand should let you return it.

Thank you! I hadn't expected helpful advice! I think I shall have to take it back, my old boots one was much better!

I haven't done anything different today. I'm beginning to think it must be the light, it's a bit gloomy in Debenhams + horrible artificial lighting.