use unsigned value

Author: jwu

lib/color4.js

@@ -289,7 +289,7 @@ color4.equals = function (a, b) {
  * @returns {Number}
  */
 color4.hex = function (a) {
-  return (a.r * 255) << 24 | (a.g * 255) << 16 | (a.b * 255) << 8 | a.a * 255;
+  return ((a.r * 255) << 24 | (a.g * 255) << 16 | (a.b * 255) << 8 | a.a * 255) >>> 0;
 };
 
 export default color4;

test/color4.spec.js

@@ -322,6 +322,10 @@ tap.test('color4', t => {
 
     t.equal(color4.hex(colorA), 0x7fff7fff);
 
+    color4.set(colorA, 1, 1, 1, 0);
+
+    t.equal(color4.hex(colorA), 0xffffff00);
+
     t.end();
   });