what do you mean by swatch -- you have an ID document set up with RGB objects?
what do you mean by placing -- you are dragging objects from one document to another (and that's where the color changes)?
i'm guessing the documents and/or objects contain mismatched color spaces and your Color Settings are set up to ignore profiles
in essence, the color management system (CMS) is assuming/applying the default RGB color profile/space and CMS's conversion to the monitor profile is changing the screen preview because the wrong object profile is being used
one way to be catch a profile issue would be to set your Color Settings like this (and see if a Mismatch or Missing Profile warning is triggered when you try to duplicate the problem)
I don't know how to stop it doing this I would be REALLY grateful if someone could explain this to me!
Set your Transparency Blend Space to RGB. Just keep in mind that if the document destination is print the color will have to be converted to CMYK at export or output.
I have the exact same issue. When I'm adding an image to my document, the colours become darker for some reason. When I delete the image, the colours go back to normal. Does anyone have any idea how this can be solved?
What's your Edit>Transparency Blend Space set to?
The issue has been solved. The reason was that the image had a RGB colour profile, and the document a CMYK colour profile. I changed the colour profile of the image in Photoshop, and it was solved.