The Cokin Filter P661 Gradual Fluo Yellow 2 is for half covered with a yellow colour that with a soft gradient passes to the other half without effect. This filter is ideal for certain colours in the picture to emphasize or to obtain a colour contrast as for example in landscape and car photography. You decide where in the photo the filter has an effect by shifting the position of the filter in the filter holder. It is also possible to combine two graduated filters with each other. If you combine filters you can have several colours flow into each other.
Cokin graduated filters are available in two densities 1 & 2, with #2 being darker.