I have just received a Concert set - I was surprised to see they are distinctly grey, not black. I thought for a minute I had received a pack of the Lava strings by mistake. Comparing the colour with a Lava set I have and they are very similar, but the feel is totally different. They feel very similar to the red series strings. They have gone straight onto my Mahogany Howlett - quick initiative impressions are that they settle into tune very quickly (but I note from Doc_J above that the sound may change after they have been played in a while); they are certainly bright - similar to the reds, but maybe a touch more mellow. A cross between the red's and the lava's...... Once played in I may do a quick sound sample.
Ziegenspeck Spruce Tenor, Howlett Mahogany Concert, Alder Concert, Big Island Koa Concert, WOU Acacia Soprano, Hamano Mahogany Soprano, Acacia Sopranino, Tenor Cigar box, Risa Stick Soprano.