Would this color combinations (RGB)have to be learnt

Answer 1

I don't think so.
Just learn some basic colors codes.
Remember some thinks like:
When all values are equal then it gives different shades of gray.

Eg-
rgb(255, 0, 0) is displayed as red, because red is set to its highest value (255) and the others are set to 0.

You can visit:
https://www.w3schools.com/html/html_colors.asp

Answer 2

You can try also this tool i made to convert from RGB colors yo hexadecimal values

https://code.sololearn.com/W8G63EN3PtJt/?ref=app