I simply tend to use web safe colours so that there is less chance of them appearing differently depending on browser and operating system. It might not be as much of an issue these days but old habits die hard (I'm old) and beside this help make colours more consistent across flags:
Web safe color codes chart. Web safe RGB color hex codes. Web safe 216 colors palette.
www.rapidtables.com
One of the advantage of limiting your colour palette is that you quickly see if a design works or not by looking at contrast between "very pale-pale-medium-dark-very dark" colours rather than 16 millions variation of them.