I know this sounds like a weird question (and my instinct says there is no way Google could justify such an action)... but...
recently I've been having a look at my adsense to see if I can optimize it a little more. I went through a few different colors variations before working out that I pretty much had it right the first time. The only thing I did notice was if the color you select is too close to the background color then google automatically changes it to the nearest contrasting shade.

For example, my adsense URLs were too light against the background so google had automatically been toning up the color I selected. I never noticed this when I originally did this over a year ago but this time when going back to my original pallette I change what I had selected as the URL color to what google was replacing it with (I used a color dropper so the color would be identical).

So the pallette colors are now identical right....? (only google isn't making color substitutions). Since doing this the CTR has stayed the same but the eCPM has gone up between 40 - 50 cents?

This is probably a coincidence and by no means am I complaining, but it does (in my mind) raise the questions:
Does Google view the act of trying to merge certain elements too well into the website design as trying to cheat the system? Is there an automatic penalty if Adsense has to reconfigure colors?

Thought I'd post this just to see if anyone else had experienced this?