What colour was the פרה אדומה?
We find in the Torah and Chazal , the colour “אדום” can be translated
a) the actual red colour (red wine)
b) the red family, colour (brown , orange etc.)
(Bereishis 25 : 30) הלעיטני נא מן האדום האדום הזה
It is called red lentils, but its colour is brown.
(Zecharya 1:8) איש רוכב על סוס אדום - סוסים אדומים –
(A man riding on a red horse-red horses)
There are no red horses .There are brown horses.
(Succah 35b) An Esrog that was peeled and looks like a red date.
Rashi explains, "All peeled fruits נהפך לאדמימות" (turn red).
Peeled or cut fruits turn brown not red.
(Bechoros 6a Rashi) סתם סוסים אדומים (horses are usually red)
Never heard of red horses
The colour of a פרה אדומה was not fire engine red nor red wine red.
There are no red cows and probably never was
The cow was brown .The uniqueness of the Para Aduma
was not that it was red. It was unique by being completely
brown, not having two strands of hair in a different colour
other than brown.(white-black)
One might argue and claim it stil needs to be a certain shade
of brown (orange or light brown etc,) However we don't
find in the Rambam qualifying what shade of אדום is כשר.
If we assume אדומה is brown there is no reason to to insist it to
be a specific shade.
Therefore it wasn't a "red heifer" but a "brown cow"