greyish-black vs grey-black

greyish-black and grey-black both are adjectives.

Word	Noun	Adjective	Verb	Adverb
greyish-black	No	Yes	No	No
grey-black	No	Yes	No	No

As adjectives, greyish-black and grey-black are synonyms defined as:

Other synonyms of greyish-black include gray-black, grayish-black.

greyish-black (adjective)	grey-black (adjective)
of black tinged with grey	of black tinged with grey