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The HSI conversion will take valid intensity values and convert them to RGB bytes > 255.

Also, shifting the intensity by a small amount can produce a rather large change in hue.

const cs = require('color-space');

console.log('HSI:');
let rgb1 = [ 0xb7, 0xc7, 0xff ];
let hsi = cs.rgb.hsi(rgb1);
let rgb2 = cs.hsi.rgb(hsi);
console.log(`     from RGB ${round(rgb1)} to HSI ${round(hsi)}`);
console.log(`  back to RGB ${round(rgb2)}`);
hsi[2] += 6;
let rgb3 = cs.hsi.rgb(hsi);
console.log(`  i+=6 to RGB ${round(rgb3)}`);

function round(vals) {
    return [Math.round(vals[0]), Math.round(vals[1]), Math.round(vals[2])];
}

Yields:

HSI:
     from RGB 183,199,255 to HSI 228,14,212
  back to RGB 183,199,255
  i+=6 to RGB 188,205,262