This is actually typical issue where users and technicians are separated. Tons of users think, they know it all, but really don't know anything. No offense, let me explain.

While users often think, they see letters and number and colors on the screen and that is what the device handles as well, the truth is, these are electronic devices that don't know letters and numbers and colors and they only know power and no power. Meaning, there is no color in storage. Which is what a file is. A file represents data on the hard drive. Which still is being stored in some representation of power and no power, not letters, numbers and colors.

This means, that the data is being interpreted in such a way, that it is being DISPLAYED in color on your monitor, but it is not actually color in storage. There is some code that tells the device, that certain parts are not text to output, but formatting. Also meaning, that displaying data in color depends on an INTERPRETER, aka the application that makes use of the data, that distinguishes between formatting and text in the data! It also means, that interpretations can be different from interpreter to interpreter.

That said, you mention a specific example FbBlack. To me, this immediately reminds me about codes that are being used to display colored text in LINUX SHELLS like bash or fish.

What that means is, you can actually write this into pretty much ANY file, even text file. But there is a difference between opening it in a text editor or in, say, the web browser. If you open it with a text editor, the text editor doesn't handle color and will interpret everything in the file as output text and thus will show the formatting instructions as output text as well. But in case you read the text from the file with your programming language, in this case JavaScript, and output the text with the code in a shell like bash, bash or fish will interpret the code as instruction instead of output text and instead of showing the code as text, display the following code in color.

This is the same for ALL formats actually and Quentin failed to explain this properly. The difference between color and no color is actually not text file vs. HTML file or RTF. You can write text in HTML files all day and it won't display in color, just because the file name ends in .html. The difference is actually the viewer you use and more specifically, how it interprets the data. Because if you open HTML in a text editor, you will see the HTML tags as plain text and if you open the HTML file in a browser, they will be interpreted as tags, thus formatting, rather than plain output text.

Frankly, the extension helps WINDOWS (not Linux for example) to determine which application to open it with to make sure it is being interpreted correctly. The truth is, the extension does not force you to actually put the correct data and format into the file. Therefore, you don't actually have to use RTF or HTML. Even less so, if you want to output the text in the console. But it would be appropriate to use the fitting file extension for the instructions you used in the file.

(You should take your own advice, Quentin! Combined glyphs? Wrong interpretation? Talking around the topic for nothing...)