All adjustment properties of the ColorAdjust class are in the range [-1 .. +1] with an origo of 0.

According to the JavaDoc, however, the contrast property, is an exception to this rule, as it falls in the less intuitive range [0.25 .. 4] with an origo of 1. From a developer perspective this is error prone and more difficult to work with.

For uniformity, I suggest you rework the contrast property to be identical with the other properties having a range of [-1 .. +1] and an origo of 0.

Since this will break backwards compatibility, I think 2.0 is a good time to fix this.