Tiffen Graduated Color Filters are half color graduating to half clear without a distinctive harsh line. They add color (or reduce exposure) to part of a scene leaving the remainder uneffected
They are available in most popular sizes in the following varieties:
Graduated Blue -- To deepen sky or water scenes.
Graduated Sunrise -- Adds dramatic sunrise to lackluster morning shots.
Graduated Neutral Density .6 (2X medium) -- Evenly reduces the light of half the picture. Effective when mixed lighting will produce a partially under or over exposured scene.