These 2 separate characters express two different ideas or do they?
They are pronounced Bi with the 4th tone.
The one on the color is a adjective meaning, depenidng on which dictionary you consult, emerald, azure, sky blue, green, jasper, or green jade. Li Ho used it in a poem to describe the color of the sky at sunset.
A green sky? or A green stone?
I think what we're seeing here is a semantic split of one word into two meanings and characters.
Consider the character on the left Bi a stone disc a symbol of authority often made of jade but also of other semiprecious stones. The word or rather the character for jade is also used in the name of gemstones that are must certainly not jade, nephrite, or jadeite.
One word to describe the color of stone or sky.
Another to describe an object some experts regard as being a solar symbol.
My theory is that the word originally meant the color of sunlight on stone. People started comparing the color of the sky to polished stones and vice versa .... then writing developed and having two separate characters lessened confusion and over the centuries one became two?
Odd idea? No odder than leaf meaning leaf of a book and leaf of a tree in English or Book in English and German being derived from the name of the birch tree because the bark was used for writing on.