Trumpy has a habit of hiring Bakster's monkeys to write painting instructions.
So, you need a grain of salt near a 1 kg salt lick when using them.
Now, yes, the presumptions is that X + Y = 50/50 mixing. Whether that resultant color even aproximates Royal Navy colours is subject to interpretation.
Arguably, the best colour match available is from Colourcoats, out of England. So a person might believe they might be a bit accurate, being British and all.
I want to say that there is an AK set of RN colours available, but I could be wrong.
When I built Rodney, my LHS had just started carrying Humbrol (enamels in the teeny tins), and I want to remember they had RN colours in their inventory.
You might want to follow this link: https://www.sovereignhobbies.co.uk/pages/british-royal-navy-colour-schemes
Especially as you are planning a KGV in the future.