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Rainbow-Gradient.md

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+The _RainbowGradient_ is one of the default gradients provided by CUE.NET.
+It's based on the color gamut of the [HSV-color space](https://en.wikipedia.org/wiki/HSL_and_HSV).  
+  
+The _RainbowGradient_ has only two properties. The [hue](https://en.wikipedia.org/wiki/Hue) of the start and end end point.  
+Both are given in degree-values for which you can take this image as reference:
+<img src="https://upload.wikimedia.org/wikipedia/commons/a/ad/HueScale.svg">
+
+> The rainbow gradient can cover more than 360 degree. To get more than one cycle of rainbow-colors just use a bigger value.
+
+If you want to create a gradient representing an rainbow cycling on and a half time through all colors (starting with red and ending with cyan), you can take the following code:
+
+```C#
+RainbowGradient rainbowGradient = new RainbowGradient(0, 540);
+```