Please excuse a "dummy" question. I have been trying to understand the use of text colours in sketch text.
If I look in the reference section I see that functions are coloured orange, variables are turquoise green and structure text is olive green.
If I click on, for example "if" (olive green) it brings up the the explanation of the syntax and example text which is coloured orange
Am I missing something obvious?
It's not clear to me what you're asking. Are you talking about the fact that the coloration in the reference pages does not match the coloration in the Arduino IDE. That is indeed unfortunate, and it has been reported to the Arduino developers already:
One thing you should know about the syntax coloration in the Arduino IDE for libraries is it is accomplished via a very crude system. Library authors can define keywords for their libraries. Some do this, others don't bother, some do it incorrectly, others do it but don't maintain their keywords list so only some of the functions of that library are colored. The Arduino IDE will color all the keywords of every library you have installed, even the libraries you're not using in your sketch. This means that once you get a lot of libraries installed you'll end up with many random words in your sketch colored.
So don't put so much meaning into the colors of text in the Arduino IDE