Explanation
This message appears when a fixture is given an HSI or CIE X/Y value that it cannot physically output, and it is outputting the closest possible color point instead.
All LED fixtures have a limited gamut of colors that they can output. This limit is determined by the colors of the individual emitters in that fixture. However, an HSI or CIE X/Y color space represents all possible colors in the visible spectrum of light. Using the color picker on a fixture, or using an HSI / CIE XY profile, will allow you to set a color point outside of this range. In Source Four LED Series 3 and Fos/4 fixtures, the fixture will report this state in the About Fixture menu.
The area inside of the polygon in this diagram represents the color gamut of the Lustr X8 emitter mix. An XY value of 0.1, 0.4, for example, would result in an Out of Gamut notification on the fixture.