This article has photographs of the roundabout itself being decorated by a local artist:
https://portal.fo/dagur-36150/myndir-listaverkid-hja-trondi-...
https://portal.fo/dagur-36150/myndir-listaverkid-hja-trondi-...
I think this might also just be an effect of the fake high dynamic range on the pictures (i.e. a rather large amount of color bleed from an underexposed slice of the image was artificially enlarged to make it "pop" more).