Colours are adjectives. And like a lot of Finnish adjectives, many (but not all) of the colours end in -nen.
Here are some colours in Finnish:
Sometimes you may want to describe a colour. Light blue, dark blue, mint green and so on. Usually, the most natural-sounding way to do this is to add a genitive word (adjective or noun) in the front.
vaalea = light (the genitive: vaalean)
vaaleansininen = light blue
tumma = dark (the genitive: tumman)
tummanvihreä = dark vihreä
taivas = the sky (the genitive: taivaan)
lohi = salmon (the genitive: lohen)
lohenpunainen = salmon red (in English this is usually called salmon pink)
minttu = mint (the genitive: mintun)