Husk of Walnut Oil aka Olio Mallo di Noce.
The husk is the fleshy part produced by the plant which is covering the fruit itself. The nuts we commonly buy at the supermarket are not quite how you would find them on the trees - they have been stripped from the husk and dried, roasted or salted. The true walnut (or endocarp) is in fact wrapped by a layer pulposus, the husk (or mesocarp), in turn covered by a peel (or exocarp).
naphthoquinones (Vitamin K compound) and juglone (aromatic compound present in naphthoquinones) found present in the cells which make up the husk. When applied these substances react with the keratin present in hair and epidermis of the skin, creating a complex brown pigmentation, explaining the use of walnut shells as a hair dye for red-brown reflections.
Immediately after application your skin will begin to look tanned purely due to the pigmenting effects of the oil properties. Once in the presence of ultraviolet radiation, the chemical complex naphthoquinone - keratin acts as selective filter, helping to shield the skin from the UVB rays as well as accelerating the melanogenesis (production of melanin) induced by UVA rays. For this reason the walnut oil is extensively used in the formulation of suncare products.
So now you know!
My recommendation: Kodrap Olio al mallo di noce - approx. 4euro a bottle in stores.