Paint color tone changing in colors
 

Hi,
I was wondering if anyone could help me figure why the color of paint in the corners my walls is changing tones. This happened rather suddenly on years-old paint over a matter of weeks. It is on most if not all corners in my house. It also happens on fresh-painted corners. I have attached a picture.
If anyone could help me figure out what is causing this, that would be great!

Yikes....looks like the corners are getting lighter?
Pretty freaky

I've seen soot and furnace blow-back accumulate along studs...even just dirt and moisture do funny things
But that doesn't turn lighter...and it's not just in corners-it 'stripes' along the wood bracing behind it on the wall/ceiling...

It there any other info you can give us about the house and/or paint used?

The plaster walls at my mom's house were doing that exact thing. I ended up giving the walls a coat of primer and then a coat of paint and they went away. She was smoking then, so I think that may have had something to do with it.