Completely self coloured, very dark purple.
There's no sign of gold streaking, is this a named cultivar?
WOW! What a cool plant. What a color!
Are they difficult to grow?
very easy. Hardy zones 5-9, doesn't like dry (unlike the germanicas), but tolerates wet. Does very well in a regular flower bed. It doesn't even need division very frequently... just plunk it in a decent spot.
They are a real gem.