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HSV color scheme
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<iframe 
    src="https://jsxgraph.org/share/iframe/hsv-color-scheme" 
    style="border: 1px solid black; overflow: hidden; width: 550px; aspect-ratio: 55 / 65;" 
    name="JSXGraph example: HSV color scheme" 
    allowfullscreen
></iframe>
This code has to 
<div id="board-0-wrapper" class="jxgbox-wrapper " style="width: 100%; ">
   <div id="board-0" class="jxgbox" style="aspect-ratio: 1 / 1; width: 100%;" data-ar="1 / 1"></div>
</div>

<script type = "text/javascript"> 
    /*
    This example is licensed under a 
    Creative Commons Attribution ShareAlike 4.0 International License.
    https://creativecommons.org/licenses/by-sa/4.0/
    
    Please note you have to mention 
    The Center of Mobile Learning with Digital Technology
    in the credits.
    */
    
    const BOARDID = 'board-0';

    var board = JXG.JSXGraph.initBoard(BOARDID, { boundingbox: [-4, 4, 4, -4], keepaspectratio: true });
    var H = board.create('slider', [[-3, 3.5], [2, 3.5], [0, 1, 360]], {
        name: 'H',
        fillColor: 'black',
        strokeColor: 'black'
    });
    var S = board.create('slider', [[-3, 3], [2, 3], [0, 1, 1]], { name: 'S', fillColor: 'black', strokeColor: 'black' });
    var V = board.create('slider', [[-3, 2.5], [2, 2.5], [0, 1, 1]], {
        name: 'V',
        fillColor: 'black',
        strokeColor: 'black'
    });
    
    var r1 = 2;
    var r2 = 1 / 4.75;
    var lambda = 8;
    
    var c1 = board.create('curve', [
             (t) => r1 * Math.sin(t) + r2 * Math.sin(lambda * t),
             (t) => r1 * Math.cos(t) + r2 * Math.cos(lambda * t) - 0.2,
             0, 2 * Math.PI
       ], {
        fillcolor: () => JXG.hsv2rgb(H.Value(), S.Value(), V.Value()),
        highlightFillcolor: () => JXG.hsv2rgb(H.Value(), S.Value(), V.Value()),
        strokeColor: 'black',
        strokeWidth: 3
    });
    
    var c2 = board.create('curve', [
              (t) => Math.sin(t),
              (t) => Math.cos(t) - 0.2,
              0, 2 * Math.PI
       ], {
        fillcolor: () => JXG.hsv2rgb(180 + H.Value(), S.Value(), V.Value()),
        highlightFillcolor: () => JXG.hsv2rgb(180 + H.Value(), S.Value(), V.Value()),
        strokeColor: 'black',
        strokewidth: 3
    });
    
    var t = board.create('text', [1, -3, () => 'RGB=' + JXG.hsv2rgb(H.Value(), S.Value(), V.Value())], { fontSize: 32 });
 </script> 
/*
This example is licensed under a 
Creative Commons Attribution ShareAlike 4.0 International License.
https://creativecommons.org/licenses/by-sa/4.0/

Please note you have to mention 
The Center of Mobile Learning with Digital Technology
in the credits.
*/

const BOARDID = 'your_div_id'; // Insert your id here!

var board = JXG.JSXGraph.initBoard(BOARDID, { boundingbox: [-4, 4, 4, -4], keepaspectratio: true });
var H = board.create('slider', [[-3, 3.5], [2, 3.5], [0, 1, 360]], {
    name: 'H',
    fillColor: 'black',
    strokeColor: 'black'
});
var S = board.create('slider', [[-3, 3], [2, 3], [0, 1, 1]], { name: 'S', fillColor: 'black', strokeColor: 'black' });
var V = board.create('slider', [[-3, 2.5], [2, 2.5], [0, 1, 1]], {
    name: 'V',
    fillColor: 'black',
    strokeColor: 'black'
});

var r1 = 2;
var r2 = 1 / 4.75;
var lambda = 8;

var c1 = board.create('curve', [
         (t) => r1 * Math.sin(t) + r2 * Math.sin(lambda * t),
         (t) => r1 * Math.cos(t) + r2 * Math.cos(lambda * t) - 0.2,
         0, 2 * Math.PI
   ], {
    fillcolor: () => JXG.hsv2rgb(H.Value(), S.Value(), V.Value()),
    highlightFillcolor: () => JXG.hsv2rgb(H.Value(), S.Value(), V.Value()),
    strokeColor: 'black',
    strokeWidth: 3
});

var c2 = board.create('curve', [
          (t) => Math.sin(t),
          (t) => Math.cos(t) - 0.2,
          0, 2 * Math.PI
   ], {
    fillcolor: () => JXG.hsv2rgb(180 + H.Value(), S.Value(), V.Value()),
    highlightFillcolor: () => JXG.hsv2rgb(180 + H.Value(), S.Value(), V.Value()),
    strokeColor: 'black',
    strokewidth: 3
});

var t = board.create('text', [1, -3, () => 'RGB=' + JXG.hsv2rgb(H.Value(), S.Value(), V.Value())], { fontSize: 32 });
<jsxgraph width="100%" aspect-ratio="1 / 1" title="HSV color scheme" description="This construction was copied from JSXGraph examples database: BTW HERE SHOULD BE A GENERATED LINKuseGlobalJS="false">
   /*
   This example is licensed under a 
   Creative Commons Attribution ShareAlike 4.0 International License.
   https://creativecommons.org/licenses/by-sa/4.0/
   
   Please note you have to mention 
   The Center of Mobile Learning with Digital Technology
   in the credits.
   */
   
   var board = JXG.JSXGraph.initBoard(BOARDID, { boundingbox: [-4, 4, 4, -4], keepaspectratio: true });
   var H = board.create('slider', [[-3, 3.5], [2, 3.5], [0, 1, 360]], {
       name: 'H',
       fillColor: 'black',
       strokeColor: 'black'
   });
   var S = board.create('slider', [[-3, 3], [2, 3], [0, 1, 1]], { name: 'S', fillColor: 'black', strokeColor: 'black' });
   var V = board.create('slider', [[-3, 2.5], [2, 2.5], [0, 1, 1]], {
       name: 'V',
       fillColor: 'black',
       strokeColor: 'black'
   });
   
   var r1 = 2;
   var r2 = 1 / 4.75;
   var lambda = 8;
   
   var c1 = board.create('curve', [
            (t) => r1 * Math.sin(t) + r2 * Math.sin(lambda * t),
            (t) => r1 * Math.cos(t) + r2 * Math.cos(lambda * t) - 0.2,
            0, 2 * Math.PI
      ], {
       fillcolor: () => JXG.hsv2rgb(H.Value(), S.Value(), V.Value()),
       highlightFillcolor: () => JXG.hsv2rgb(H.Value(), S.Value(), V.Value()),
       strokeColor: 'black',
       strokeWidth: 3
   });
   
   var c2 = board.create('curve', [
             (t) => Math.sin(t),
             (t) => Math.cos(t) - 0.2,
             0, 2 * Math.PI
      ], {
       fillcolor: () => JXG.hsv2rgb(180 + H.Value(), S.Value(), V.Value()),
       highlightFillcolor: () => JXG.hsv2rgb(180 + H.Value(), S.Value(), V.Value()),
       strokeColor: 'black',
       strokewidth: 3
   });
   
   var t = board.create('text', [1, -3, () => 'RGB=' + JXG.hsv2rgb(H.Value(), S.Value(), V.Value())], { fontSize: 32 });
</jsxgraph>
The HSV color scheme consists of three values: - Hue (base color): between 0 and 360 - Saturation (purity): between 0 and 1 - Value (brightness): between 0 and 1 Here, you can experiment with these values. The outer color is determined by the sliders, the inner color is the complementary color (adding $180^\circ$). Additionally, the (outer) HSV color is converted to RGB.
// Define the id of your board in BOARDID

var board = JXG.JSXGraph.initBoard(BOARDID, { boundingbox: [-4, 4, 4, -4], keepaspectratio: true });
var H = board.create('slider', [[-3, 3.5], [2, 3.5], [0, 1, 360]], {
    name: 'H',
    fillColor: 'black',
    strokeColor: 'black'
});
var S = board.create('slider', [[-3, 3], [2, 3], [0, 1, 1]], { name: 'S', fillColor: 'black', strokeColor: 'black' });
var V = board.create('slider', [[-3, 2.5], [2, 2.5], [0, 1, 1]], {
    name: 'V',
    fillColor: 'black',
    strokeColor: 'black'
});

var r1 = 2;
var r2 = 1 / 4.75;
var lambda = 8;

var c1 = board.create('curve', [
         (t) => r1 * Math.sin(t) + r2 * Math.sin(lambda * t),
         (t) => r1 * Math.cos(t) + r2 * Math.cos(lambda * t) - 0.2,
         0, 2 * Math.PI
   ], {
    fillcolor: () => JXG.hsv2rgb(H.Value(), S.Value(), V.Value()),
    highlightFillcolor: () => JXG.hsv2rgb(H.Value(), S.Value(), V.Value()),
    strokeColor: 'black',
    strokeWidth: 3
});

var c2 = board.create('curve', [
          (t) => Math.sin(t),
          (t) => Math.cos(t) - 0.2,
          0, 2 * Math.PI
   ], {
    fillcolor: () => JXG.hsv2rgb(180 + H.Value(), S.Value(), V.Value()),
    highlightFillcolor: () => JXG.hsv2rgb(180 + H.Value(), S.Value(), V.Value()),
    strokeColor: 'black',
    strokewidth: 3
});

var t = board.create('text', [1, -3, () => 'RGB=' + JXG.hsv2rgb(H.Value(), S.Value(), V.Value())], { fontSize: 32 });

license

This example is licensed under a Creative Commons Attribution ShareAlike 4.0 International License.
Please note you have to mention The Center of Mobile Learning with Digital Technology in the credits.