This is 100% incorrect. Not in terms of science, but in terms of a qualifier of what a colour is. Just because a colour doesn't exist on the rainbow spectrum, doesn't mean it's not an "actual colour".

What you're referring to is the definition of colour specifically by physics. There are other professional fields and areas of science that use different qualifiers for colour. I work with color everyday and I can with certainty say that purple, pink, rust, teal, and sky blue are all colours.

Kind of like how different fields have different definitions of entropy or different cultures have different names for snow. It's all dependent on the framework you use and ignoring every other framework is wrong.