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Alessandro,That looks like the more traditional "red" and yellow one from commerce. There is also a yellow form (formerly called Calostemma lutea, but now just part of purpurea) that has much more open wide flowers. Then there are ranges in between. I have posted pics in the past of red and yellow combinations elsewhere on the forum, which have the shape of the yellow but varying amounts of red in the centre. There is also a white species, which I have never yet seen in person, and a whole range of colours occurring naturally, which we never see in commerce at all unfortunately.