There are so many examples of how the Genesis six days of creation match and correspond exactly with the six physical manifestations of this world. They creation days are "six" in number. This signifies the world with it's "six directions." (east, west, north, south, up, down)
Interesting the way you work out your six by
adding up and down. The thing is, if you wanted to come out with the mystical number four, all you had to do was stick with the four compass points. Which Christians have done in the past.
There are four gospels and only four, neither more nor less: four like the points of the compass, four like the chief directions of the wind. The Church, spread all over the world, has in the gospels four pillars and four winds blowing wherever people live.
Irenaeus, Against Heresies, 2nd century
Your six directions, is really just forward and back in our good old three dimensions, each pair of directions forming a single axis, which if you are looking for the number three proves the Trinity. Of course if you really wanted the number four you can drag in Einstein and say time is the fourth dimension and science has confirmed the bible yet again.
When Noah looked at the rainbow he saw colors. When later men looked at the rainbow they tried to distinguish it's colors. The colors were the same when light shone through water/rain, and also through earth/crystal. But when light shone though crystal/earth the colors were upside down. People soon distinguished a pattern in the colors where they fit together into a color circle which alternated then as "primary color" and secondary color" alternitivaly. That is how they became seen as the six colors. It was not haphazard. It was made to be understood by thoughtful men. God provided human beings with a reasonable mental world to understand.
So why do people today think there are seven
colours in a rainbow?
Don't confuse primary and secondary
colours of modern
colour theory with either the spectrum itself. None of the different primary colour schemes. whether red yellow and blue, magenta yellow and cyan, or red green and blue, can match the violet of the rainbow.
And the number of colours people say makes up a rainbow varies from culture to culture. Homer described the rainbow as purple. Aristotle said the rainbow was made up of three colours red green and purple.
Xenophanes identified the three colours but they were crimson, yellow and blue. This was questioned by people like Seneca who claimed the number was indefinite, but Aristotle's three coloured rainbow was widely accepted in Medieval Europe and see as evidence for the Trinity. The Muslims meanwhile realised there were four colours red, yellow, green and blue representing the four elements. Chinese mythology said there were five, which is what Newton said at first too before claiming there were seven.
Noah would certainly have seen colours, but we have no idea how many colours he would have thought there were or if he would even have thought to try and identify them.