Colours in document became muddy/muggy

I created a new file in Illustrator and pulled in different layers (shape and pattern layers) from two previous documents. I closed all other tabs and left that new file open for a few hours while I worked on another file in Photoshop. When I went back to the Illustrator file I had created a few hours, all the shape and pattern layers' colours had turned muddy. When I compared the colours to the original layers from the two previous documents, there is a noticeable difference. To my knowledge, I didn't change any settings after placing these layers into the new Illustrator file or while the file sat open for those few hours. Basically, everything was fine before I left the file open for a few hours while I worked in Photoshop and then everything changed went back to the file after those few hours. All the colours were different. They looked muggier/muddy. Does anyone know why this happened?