This problem has arisen a few times and I haven't seen an answer as to why it's happening. I've had this issue where the colors in my document, whether custom colors or pulled from imported swatches, etc, change and got more dull and darker over time in the doc. It changes the hex/rgb values and everything. It's quite frustrating and I've had this happen to me on two different machines over the last 2 years. I have not changed any color settings, I am working in RGB. I link a lot of images within my document as well.
Below is one instance. I cheated the background of this image by eye dropping it and it will change to the darker version within a few hours, having not touched that composition.
Here is another instance, bottom is the original color, top is the altered.
 
These are the settings that I see, note that I did not change any Color Mangement/Profiles.
 
 
This is the color profile that I see most often.
 
But I also saw this pop up at some point, so I screenshotted it.
I will continue to monitor it and post updates as I need this to be sorted. 
Is it changing color profiles as I work? Is there some hot key that I'm accidentally hitting that I'm unaware of? And what should the color profiles be. I'm not doing production work. I'm working in RGB to create work for a digital branding presentation. Nothing that should need anything specific, I feel.
 
Good luck and godspeed.