Got into an argument over the color shade transition from the Statenvlag to the modern Dutch flag.
The guy I spoke to argued that in the 14/15th century people wouldn't be able to reproduce the same shade of color, is there any truth to that?
Your friend is wrong. Cennino Cennini's Il Libro dell' Arte clearly describes how to make specific colors.
You can see most of it here, https://books.google.com/books?id=4Z2jAQAAQBAJ
Dyeing with plants depends on the growth conditions of that year, when the plants are harvested, water temp. and which mordant is used and how. This will all give differences in hues but master dyers are able to adjust a dye bath as it's curing, amending the colour to the exact shade desired.
Especially Dutch flag colours could be reproduced exactly because the red comes from Cochineal insects and the blue from Indigo plants or Wede plants (Isatis tinctoria) , three sources which yield intense and consistent colour each year.
Royal Blue in the Dutch flag is from the first blue dye bath. Statenvlagblue is from a second or third bath.