"This merchandise is not at all the color I thought it would be"
How many times has this happened to you? Have you ever walked into the Library, or classroom and see a bank of computers that all have slightly different colors, or brightness settings. I'm sure you know that all monitors show color variations, but do your buyers?
Every one of the three monitors we have in our house show my product differently and my laptop even varies brightness by tilting the screen at a different angle.
What's a seller to do?
I have two FANTASTIC ideas to help.
Make sure that you describe the color as accurately as possible. Not just Orange but Light Burnt Orange. Not just Blue, but Robins Egg Blue, of whatever description can help your buyer identify the color correctly. If you say that the color is Robin's Egg Blue and they see Navy, they may realize that their monitor color is off.
This disclaimer was borrowed from a very wise seller. It is on every listing. You can add a similar note to your listings to help prevent problems.
"Real colors may slightly differ from their appearance on your display, as it depends on your monitor settings and is not under our control."
Both suggestions are great ideas, but the real trick is for you to get your buyer to actually READ the descriptions. If they didn't, you at least have the description to show them when they contact you to say that their purchase isn't the right color.