There is a function appropriately named HEXCOLOUR that has the hex code (without the hash symbol) as a parameter:

HEXCOLOUR("A0FF03")

There is also another function that takes the name of the color, but only works with a limited set of names:

NCOLOUR("WHITE")

The color RGB is the same like Hex code.

The code in RGB is representable betwen 0 to 255 in decimal for each color (red, green and blue).

So for example RGB = 255,144,29 is the same like Hex = FF901D (R: 255>FF | G:144>90 | B:29>1D)

But like Rodrigo said you ofcourse have a function with name HEXCOLOUR.