Correlation and causation are two separate things. In this case, I believe you have correlation, but not causation. I would be more apt to believe its a bulb change, or something else rather than adding the other clown that has been causing the color shift. You may now be more aware of changes, however, as you are likely studying your fish now after your recent purchase, and this believe you are seeing dramatic changes.
It is common, btw, for ocellaris to get a "sun tan" where the top part of the body appears to have a dark hue.