The hoya yellowgreen x0 hoya multi coated hmc glass filter has an effect similar to that of the medium yellow filter but it also darkens red colours clouds in the sky gain more contrast a red roof and red flowers are rendered darker in relation to plant greens as they would not with a purely yellow filter the yellow green filter accentuates the delicate springtime green in nature it makes portraits more dramatic need more contrast in your black and white want a more dramatic apri