wheat vs yellowness

wheat and yellowness both are nouns.

Word	Noun	Adjective	Verb	Adverb
wheat	Yes	No	No	No
yellowness	Yes	No	No	No

As nouns, yellowness is a hypernym of wheat; that is, yellowness is a word with a broader meaning than wheat:

wheat: a variable yellow tint; dull yellow, often diluted with white
yellowness: yellow color or pigment; the chromatic color resembling the hue of sunflowers or ripe lemons

Other hypernyms of wheat include yellow.

wheat (noun)	yellowness (noun)
a variable yellow tint; dull yellow, often diluted with white	yellow color or pigment; the chromatic color resembling the hue of sunflowers or ripe lemons
grains of common wheat; sometimes cooked whole or cracked as cereal; usually ground into flour
annual or biennial grass having erect flower spikes and light brown grains