In Scottish Gaelic too. There's a good research piece here on how Gaels see colour
pure.uhi.ac.uk/en/publicati...

It's indeed correct, derived from 'iasg' meaning fish

@frankrennie.bsky.social

Our neighbouring village (in the North of the Isle of Lewis) put an eel to work keeping the holy well clean. Presumably all the algae it could eat.

Iceland has an issue with lupin too I think, a lovely lavender shade but invasive.

Long traditions of using it in Gaelic medicine and as a dye, but does seem to have taken a growth spurt in the last few years in the Hebrides. Not at rhododendron levels yet though...