The airport in Minneapolis is expensive and reasonably thoughtful in its design.
But the signs are monochromatic. As a result, the tired traveler wanders in circles, looking for her destination. Imagine how much easier it would be to find out where you were going if every sign with the word TAXI on it had it in yellow instead of white. Once you knew the color of where you were going, you'd just naturally scan for it.
Google and our text-based low-res online world seems to argue against color as a signal, but it's extraordinarily powerful. You don't need to make a big deal of of it, subtle is enough. Make the button you want pressed green on every page. Soon, your users will naturally gravitate to green buttons…
This works in Powerpoint presentations and even contracts. A little goes a long way.