The spellings of the devil's bit scabious and spotted orchid are rather convoluted. But the scabious is most likely based on the root odhar (compare Irish, which is fairly consistent in the use of odhrach bhallach for the devil's-bit scabious) i.e. the 'dusky globed one' whereas ùrach-bhallach (and variants) is most likely the 'fresh balled one' (ùr » ùrach) or 'earth balls' (ùir » ùireach/ùrach).The scabious is not dusky or dun but the reference may be to its traditional use in healing bruises and skin sores.

Also compare the etymology of orchid from Greek ὄρχις 'testicle'. Of the sparse fieldwork data, both incidents of forms of ùrach-bhallach (both from DASG) refer to orchids, not the scabious.