Color Palette Generator

// Generate a complementary color by rotating hue 180 degrees
function hexToHsl(hex) {
  let r = parseInt(hex.slice(1,3), 16) / 255;
  let g = parseInt(hex.slice(3,5), 16) / 255;
  let b = parseInt(hex.slice(5,7), 16) / 255;
  const max = Math.max(r,g,b), min = Math.min(r,g,b);
  let h = 0, s = 0, l = (max + min) / 2;
  if (max !== min) {
    const d = max - min;
    s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
    if (max === r) h = ((g - b) / d + (g < b ? 6 : 0)) / 6;
    else if (max === g) h = ((b - r) / d + 2) / 6;
    else h = ((r - g) / d + 4) / 6;
  }
  return [Math.round(h * 360), Math.round(s * 100), Math.round(l * 100)];
}

function hslToHex(h, s, l) {
  s /= 100; l /= 100;
  const a = s * Math.min(l, 1 - l);
  const f = n => {
    const k = (n + h / 30) % 12;
    return Math.round(255 * (l - a * Math.max(-1, Math.min(k - 3, 9 - k, 1))));
  };
  return '#' + [f(0), f(8), f(4)].map(v => v.toString(16).padStart(2, '0')).join('');
}

const base = '#6366f1';
const [h, s, l] = hexToHsl(base);
const comp = hslToHex((h + 180) % 360, s, l);
console.log(comp); // → "#f1ee63"

import colorsys

def hex_to_hsl(hex_color: str):
    r, g, b = (int(hex_color[i:i+2], 16) / 255 for i in (1, 3, 5))
    h, l, s = colorsys.rgb_to_hls(r, g, b)
    return round(h * 360), round(s * 100), round(l * 100)

def hsl_to_hex(h: int, s: int, l: int) -> str:
    r, g, b = colorsys.hls_to_rgb(h / 360, l / 100, s / 100)
    return '#{:02x}{:02x}{:02x}'.format(round(r * 255), round(g * 255), round(b * 255))

def complementary(hex_color: str) -> str:
    h, s, l = hex_to_hsl(hex_color)
    return hsl_to_hex((h + 180) % 360, s, l)

def triadic(hex_color: str) -> list[str]:
    h, s, l = hex_to_hsl(hex_color)
    return [hex_color, hsl_to_hex((h + 120) % 360, s, l), hsl_to_hex((h + 240) % 360, s, l)]

print(complementary('#6366f1'))  # → #f1ee63
print(triadic('#6366f1'))        # → ['#6366f1', '#66f163', '#f16366']

package main

import (
	"fmt"
	"math"
)

func hexToHSL(hex string) (float64, float64, float64) {
	var r, g, b uint8
	fmt.Sscanf(hex, "#%02x%02x%02x", &r, &g, &b)
	rf, gf, bf := float64(r)/255, float64(g)/255, float64(b)/255
	max := math.Max(rf, math.Max(gf, bf))
	min := math.Min(rf, math.Min(gf, bf))
	l := (max + min) / 2
	if max == min {
		return 0, 0, l * 100
	}
	d := max - min
	s := d / (2 - max - min)
	if l <= 0.5 {
		s = d / (max + min)
	}
	var h float64
	switch max {
	case rf:
		h = (gf - bf) / d
		if gf < bf { h += 6 }
	case gf:
		h = (bf-rf)/d + 2
	case bf:
		h = (rf-gf)/d + 4
	}
	return h * 60, s * 100, l * 100
}

func hslToHex(h, s, l float64) string {
	s /= 100; l /= 100
	a := s * math.Min(l, 1-l)
	f := func(n float64) uint8 {
		k := math.Mod(n+h/30, 12)
		return uint8(255 * (l - a*math.Max(-1, math.Min(math.Min(k-3, 9-k), 1))))
	}
	return fmt.Sprintf("#%02x%02x%02x", f(0), f(8), f(4))
}

func main() {
	h, s, l := hexToHSL("#6366f1")
	comp := hslToHex(math.Mod(h+180, 360), s, l)
	fmt.Println(comp) // → #f1ee63
}