feat: add {get|set}AccentColor on Windows (#48017)

* feat: add setAccentColor on Windows

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

* refactor: unify GetSystemAccentColor

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

* refactor: remove redundant parsing

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

* chore: fixup documentation

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

* Update docs/api/browser-window.md

Co-authored-by: Will Anderson <andersonw@dropbox.com>

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

* Update docs/api/base-window.md

Co-authored-by: Will Anderson <andersonw@dropbox.com>

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

---------

Co-authored-by: trop[bot] <37223003+trop[bot]@users.noreply.github.com>
Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

spec/api-browser-window-spec.ts

@@ -2523,6 +2523,92 @@ describe('BrowserWindow module', () => {
     });
   });
 
+  ifdescribe(process.platform === 'win32')('BrowserWindow.{get|set}AccentColor', () => {
+    afterEach(closeAllWindows);
+
+    it('throws if called with an invalid parameter', () => {
+      const w = new BrowserWindow({ show: false });
+      expect(() => {
+        // @ts-ignore this is wrong on purpose.
+        w.setAccentColor([1, 2, 3]);
+      }).to.throw('Invalid accent color value - must be a string or boolean');
+    });
+
+    it('returns the accent color after setting it to a string', () => {
+      const w = new BrowserWindow({ show: false });
+      const testColor = '#FF0000';
+      w.setAccentColor(testColor);
+      const accentColor = w.getAccentColor();
+      expect(accentColor).to.be.a('string');
+      expect(accentColor).to.equal(testColor);
+    });
+
+    it('returns the accent color after setting it to false', () => {
+      const w = new BrowserWindow({ show: false });
+      w.setAccentColor(false);
+      const accentColor = w.getAccentColor();
+      expect(accentColor).to.be.a('boolean');
+      expect(accentColor).to.equal(false);
+    });
+
+    it('returns a system color when set to true', () => {
+      const w = new BrowserWindow({ show: false });
+      w.setAccentColor(true);
+      const accentColor = w.getAccentColor();
+      expect(accentColor).to.be.a('string');
+      expect(accentColor).to.match(/^#[0-9A-F]{6}$/i);
+    });
+
+    it('returns the correct accent color after multiple changes', () => {
+      const w = new BrowserWindow({ show: false });
+
+      const testColor1 = '#00FF00';
+      w.setAccentColor(testColor1);
+      expect(w.getAccentColor()).to.equal(testColor1);
+
+      w.setAccentColor(false);
+      expect(w.getAccentColor()).to.equal(false);
+
+      const testColor2 = '#0000FF';
+      w.setAccentColor(testColor2);
+      expect(w.getAccentColor()).to.equal(testColor2);
+
+      w.setAccentColor(true);
+      const systemColor = w.getAccentColor();
+      expect(systemColor).to.be.a('string');
+      expect(systemColor).to.match(/^#[0-9A-F]{6}$/i);
+    });
+
+    it('handles CSS color names correctly', () => {
+      const w = new BrowserWindow({ show: false });
+      const testColor = 'red';
+      w.setAccentColor(testColor);
+      const accentColor = w.getAccentColor();
+      expect(accentColor).to.be.a('string');
+      expect(accentColor).to.equal('#FF0000');
+    });
+
+    it('handles RGB color values correctly', () => {
+      const w = new BrowserWindow({ show: false });
+      const testColor = 'rgb(255, 128, 0)';
+      w.setAccentColor(testColor);
+      const accentColor = w.getAccentColor();
+      expect(accentColor).to.be.a('string');
+      expect(accentColor).to.equal('#FF8000');
+    });
+
+    it('persists accent color across window operations', () => {
+      const w = new BrowserWindow({ show: false });
+      const testColor = '#ABCDEF';
+      w.setAccentColor(testColor);
+
+      w.show();
+      w.hide();
+
+      expect(w.getAccentColor()).to.equal(testColor);
+    });
+  });
+
   describe('BrowserWindow.setAlwaysOnTop(flag, level)', () => {
     let w: BrowserWindow;