Birdsfoot Trefoil

Usually one can expect Trefoil to be a uniform lemon-yellow flower but occasionally I have seen it with tinges of red and orange.

I came across a whole clump this colour and had to take a picture. I wonder if the drought conditions and stress have something to do with the change. The strange thing was that the one darker clump was surrounded by other clumps that were all the usual bright yellow. Whatever the reason for it, I think it's beautiful.