Unfortunately, there is a problem with requests to change a color to some other well specified and characterized color (eg, a car factory paint code).
The problem is that the color the camera records in a photo of an object reflects (pun intended) not only its own color, but the color of the light that is illuminating it, as well as the brightness / darkness of the exposure used, and the specific color response curves for the camera's sensor, the camera's automatic white balance algorithm, the slight color cast that every lens imparts, etc. etc.
To give a specific example, suppose we took a photo of a perfectly neutral gray (128, 128, 128) when the sun was behind a cloud, and then a moment later, we take another picture after the sun emerged from behind the cloud. In the first photo, no matter how good the camera's white balance system is, the camera will almost certainly record the gray as having a bluish-cyan tint, say (128, 140, 140), whereas in the second, the camera will almost certainly record the gray as being warmer or more yellowish, say, (140, 140, 128).
In addition to changes in the color, the brightness of the gray will certainly also be different between the two shots depending on the details and settings of the camera's auto exposure system and how much of the background is included in the photos besides the main area of interest. These effects are not small, especially if you are not only changing the illumination between the two photos, but changing the camera, as well.
So, this means that if someone (i.e., you, LOL) asks me to make part of an arbitrary, non-color managed photo look like it was painted in the same (128,128,128) neutral gray discussed above, if I use the color you ask for it won't be correct (either in hue & saturation, or in brightness) for most photos.
The way this problem is minimized by pro photographers is to always include a color reference chart in every photo for which accurate colors are required and then making all these color come out correctly in both photos. One of the best known of these is the Macbeth color reference chart:
... but others are now being sold by companies such as X-rite know primarily for monitor calibration systems.
The above is a long way of saying that I don't touch such requests for accurate standardized colors in photos because I know I am almost guaranteed to be wrong unless appropriate care in color management has been given to the photos under question (eg, a calibration target included in both images, the two camera's have both been profiled and calibrated, etc. etc.).
That being said, some simplified compromise approaches are possible (eg, using only a gray card, not a multi-color reference card or using only white balance and paying no attention to the colors of the mid-grays and shadow areas), but they are rarely as accurate as handling color management correctly from start to finish.
Sorry I can't be more encouraging. You made a very reasonable request, but to truly match product colors requires considerable specialized knowledge and skills. This is one reason why competent professional commercial product photographers can command such high fees.
Tom M
