MrToM - Much of your advice in this thread (eg, problems with green screens, uncalibrated displays, etc.) is correct, but I have to take issue with two of your points.
...and isn't as critical as you may think.
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... I wouldn't be too particular about getting colours absolutely spot on.....
...but I wouldn't waste time trying to get it exact....as close as possible would be more than adequate.
I’m sorry, but in my opinion, the above comments are at complete variance with standard industry practice. The OP is exactly right in his quest for color accuracy in advertising.
In fact, there are a lot of very well paid product photographers who would probably even chuckle at the above quotation because the end result of other photographers and graphic artists not paying close attention to color is exactly what drives serious advertising customers (i.e., not the low end shops on the bay of E's) right into their arms, LOL. If you don't have experience in this field, and have not had endless discussions on this topic with editors, art directors, product specialists, etc., you simply don't realize how important accurate colors are in the advertising community.
For example, the desire for color accuracy in advertising is precisely what drove the development of things like the Pantone system and Adobe's color management system. Do you think such complicated procedures would have been developed and adopted if color wasn't of critical importance to Adobe's most important (pro) customers and the entire printing and paint industry?
To make matters worse, the need for color accuracy becomes even more important whenever well-known "memory" colors (e.g., skin, neutrals, blue sky, vegetation) are present alongside the color of the product. This is because the eye will subconsciously use the "memory colors" as references to evaluate the color of the product.
Imagine that there is a model standing next to a new model of car being advertised. It goes without saying that neutral colors better reproduce as neutral, and her skin color has to be spot on to be appealing to viewers. Now, if you want to use this base image to illustrate cars of other colors and the person who did the color changes on the car only did an approximate job, there are going to be tremendous repercussions when customers walk in to the dealership and say, "it just didn't look that way in the ad" and walk out. Manufacturers don't like it when sales worth tens of thousands of dollars walk out the door. They do everything in their power to avoid this.
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...Furthermore, each 'browser' used may not have its colour space set correctly....I mean who does that unless you know about it?...
If the image being viewed is sRGB, every popular browser will render it correctly. As far as I know, even if one intentionally tries to muck up the color settings in browsers like Firefox, these browsers will still always get sRGB right and send the correct numbers to the viewer's display system. The bottom line is that if the person doing the artwork knows what they are doing and delivers an sRGB product, there is absolutely no need for the buying public to be concerned about the color settings in browsers. Such settings only are of concern when non-sRGB color spaces are used, and this typically only is an issue to photographers and graphic artists.
Tom M