Some years ago, when computers supported max 256 different colors, a list of 216 "Web Safe Colors" was suggested as a Web standard, reserving 40 fixed system colors.
The 216 cross-browser color pallette was created to ensure that all computers would display the colors correctly when running a 256 color pallette.
This is not important today, since most computers can display millions of different colors. This is the list:
web color > web safe colors