Explaining this would require a longwinded article on the differences in Gamma between the systems and color management. That's the short version. You can find enough info on that on the Internet, but of course none of it helps you if you both don't work with actual color management and calibration. That's what it boils down to and at that point you could just as well give up. Business computers for presentations are usually not color managed and that's where everything falls apart. So your time is better spent figuring out what settings your client actually uses and tweaking your content to his crooked settings as wel las possibly advising him on how to change settings on his system to improve color rendition.And of course the old gag applies, regardless: Super-intense colors like your bright yellow will generally look wonky across different systems. Latest if you were to create content for mobvile devices based on your presentation designs you'd face the same issues again. You have to find a good middleground here and accept that colors will always be slightly off one way or the other.