I suppose colored pencils are akin to wax crayons and are basic visual aids for those not fully weaned from their use in the explanation of complex problems that require the understanding of higher forms of math in order to achieve more precise understanding of the principles governing helicopter aerodynamics.
Did the many exams inflicted upon our British fellows fail somehow to elicit a more detailed grasp of those principles than might be garnered from the results of delving into for's reading list?
I am of the thought the colored pencil brigade may have imposed unintended limits upon the desired outcome even allowing for the basic assumption their transfer of knowledge was satisfactory for practical purposes despite failing to arise to the level one might obtain elsewhere and by different methods and different instructors.
One thing for sure is those believers in the pencils do not care to be challenged or alas contradicted.
One thing I learned very early in my flying career was I can always learn something from others no matter who they are or how much experience they have.....even if the teaching point is only to never to do it the way they did.
The reading list offered by fdr points us to some very useful information although I am not sure the FAA would on my list of favorites.
I always found it useful to re-read the wonderful small Sikorsky Blue Booklet on Helicopter Aerodynamics as it was written in language that was easily understood.