Each field of keywords.txt is separated by a single true tab. Leading spaces on a keyword identifier causes it to not be recognized by the Arduino IDE. On Arduino IDE 1.6.5 and newer an unrecognized keyword identifier causes the default editor.function.style highlighting to be used (as with KEYWORD2, KEYWORD3).
Reference:
https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification#keywords
A popular library installation technique is to download the library via GitHub's Clone or download > Download ZIP and then use the Arduino IDE's Sketch > Include Library > Add .ZIP Library on the downloaded file. This requires the library to be in the root of the repository, not in a subfolder. If the library is not in the root of the repository this installation technique fails:
Specified folder/zip file does not contain a valid library
This is the standard repository structure used in all official Arduino libraries:
https://github.com/arduino-libraries
This move is also required if you wanted to add your library to the Arduino Library Manager index, which provides an even easier installation option.
