When I was in college I had a list of steps to color correct an illustration for a specific printer so it was closer to what I saw on my monitor. You could do that if you were able to sit down at the destination screen and compare the two side-by-side, but that’s not practical. I just have to tell clients, “Your screen is not calibrated, mine is, meaning my screen will be closest to the average costumer.” I actually don’t know if that statement is true. I find 80% of monitors to be too bright, PCs in particular, but logically it makes sense so the client will stop worrying about it.
The only way to make sure that color is consistent on all monitors is to use a colorimeter on each display. The Spyder colorimeters are fantastic, and I recall the license being a site license, not an individual computer license, so you can make sure color is calibrated across all machines. I also understand that the device itself works with DisplayCAL, which is open source. Monitor calibration takes about 5 minutes (it’s automatic) so you can probably do that on a client’s machine once and then you don’t have to worry about it from then on.
If you don’t have the money for a Spyder, or if they don’t want software to be installed on their computer, this site is a good resource: http://www.lagom.nl/lcd-test/ It’s a series of display patterns to make sure monitors are close enough to the standard. If the display has decent controls that let you adjust brightness, contrast and white point, those test patterns and some tinkering will take your 90% of the way there.
As you can tell, all of these solutions involve access to the client’s monitor for about a good 10 minutes. So if that can’t be done, you just have to (repeatedly) explain that the colors do look better on your monitor because it is calibrated.