fix: toHex not working (#47)

lib/helpers.js

@@ -9,6 +9,7 @@
 
 import Color from 'art/core/color';
 import Transform from 'art/core/transform';
+import {Platform} from 'react-native';
 import type {
   Alignment,
   Brush,
@@ -73,12 +74,26 @@ export function extractTransform(props: TransformProps): Array<number> {
   ];
 }
 
+function toHex(color: Color) {
+  const intValues = [color.red, color.green, color.blue];
+  if (color.alpha < 1) {
+    // Android uses AARRGGBB ; iOS uses RRGGBBAA
+    // https://developer.android.com/reference/android/graphics/Color.html#parseColor(java.lang.String)
+    const position = Platform.OS === 'android' ? 0 : 3;
+    intValues.splice(position, 0, Math.round(color.alpha * 255));
+  }
+  const hexValues = intValues.map(iv => {
+    const sv = iv.toString(16);
+    return sv.length === 1 ? '0' + sv : sv;
+  });
+  return '#' + hexValues.join('');
+}
+
 export function extractColor(color?: ColorType) {
   if (color == null) {
     return null;
   }
-  const c = new Color(color);
-  return c.toHEX();
+  return toHex(new Color(color));
 }
 
 export function extractStrokeJoin(strokeJoin?: StrokeJoin) {