I saw an old (2010) question by Henderson about the use of 'void RGB' in a programme, without a useful solution. Now I ran into the same problem, and found out what the answer should have been.
It is about the use of subroutines. You have to understand that at the end of a programme subroutines can be added with the void statement that will be executed when called for in the program itself. so, 'void RGB' is this subroutine that is called for several times in the programme.
your eureka moment ?? May be a moderator can unlock the post from 2010 and you can bring the solution to the poor lad who has been waiting 14 years to get answers ! 
(void is not a statement. what you are talking about are functions)
Hello oppe1
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Take a view to gain the knowledge.
https://www.learncpp.com/cpp-tutorial/introduction-to-functions/
Have a nice day and enjoy coding in C++.
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