Origin and usage
The adjective greenish is formed from the adjective ‘green’ plus the suffix ‘-ish’. It is older than you might think, having first been used in the late 14th century.
Something that is greenish is slightly green or of a colour similar to green. There is another form, greeny, that has the same meaning. Greeny is more recent, dating from the late 16th century. In addition to being older, greenish is also more frequently used; about 15 times as frequent as greeny in our corpus. It is usual to be able to modify colour terms in this way to indicate a colour that is adjacent to the main colour but not exactly the same as it: things can be yellowish, bluish, purplish, greyish, and so on. The alternative form with -y is available for most of the central colour words – you can say that something is yellowy or bluey or purply – and is almost always less frequent. For less common colour terms the picture is less clear. You can describe something as silvery or silverish, but ‘silvery’ is much more frequent even if we take account of the second meaning. Something can be crimsonish or crimsony, it seems, but not *scarletish or *scarlety. There are lots of entries for colour terms in Macmillan Dictionary, many of them with illustrations. You can explore them here.
“The new tiles appear white and have a faint greenish tinge that we really like.”
“The outside of the flower is greenish yellow at the base and pale yellow at the top.”
“Females are similar, but duller greeny blue.”
bluish, brownish, pinkish, reddish