Select a theme: https://primer.style/primitives/colors/ and scrap it's variables

gh-colors-scrapper.js

function colorName(c) {
  if (c.startsWith("#")) {
    return `Color(0xff${c.substr(1, c.length)})`;
  } else {
    const color = c.split(/(\(|\))/g)[2];
    return `Color.fromRGBO(${color})`;
  }
}

function varName(c) {
  const lower = c.toLowerCase();
  const fUpper = lower[0].toUpperCase();
  const name = `${fUpper}${lower.substr(1, lower.length)}`;
  return `k${name}`;
}

function colorName(c) {
  if (c.startsWith("#")) {
    return `Color(0xff${c.substr(1, c.length)})`;
  } else if (c.startsWith("rgba")) {
    const color = c.split(/(\(|\))/g)[2];
    return `Color.fromRGBO(${color})`;
  } else {
    const color = c.split(/(\(|\))/g)[2];

    const [h, s, l, a] = color
      .split(",")
      .map((x) => parseFloat(x.replace("%", "")));

    return `HSLColor.fromAHSL(${a}, ${h}, ${s / 100}, ${l / 100}).toColor()`;
  }
}

const mapper = {};

function registerVar(node) {
  const [k, v] = node[0].textContent.split(".");
  const name = varName(k);
  if (name === "kShadow") return;
  const color = colorName(node[2].textContent);
  mapper[name] = [...(mapper[name] ?? []), { variant: v, value: color }];
}

const nodes = [...document.querySelectorAll(".Box-nv15kw-0.hUGesT")];
const childNodes = nodes
  .map((n) => [...n.children])
  .filter((n) => n.length === 4)
  .map((n) => n.slice(1, n.length));

for (const node of childNodes) {
  registerVar(node);
}

let generatedCode = ``;

for (const [k, v] of Object.entries(mapper)) {
  const hsl = v.some(({ value }) => value.includes("HSL"));
  const varType = hsl ? "final" : "const";

  generatedCode += `${varType} ${k} = <String, Color>{
    ${v
      .map(
        ({ variant, value }) => `'${variant}': ${hsl ? "const" : ""} ${value}`
      )
      .join(",\n  ")}
  };\n\n`;
}