fix serialize awt color

extension/src/main/java/com/alibaba/fastjson2/support/AwtWriterModule.java

@@ -18,7 +18,10 @@ public class AwtWriterModule
     public ObjectWriter getObjectWriter(Type objectType, Class objectClass) {
         if (objectType == Color.class) {
             return objectWriter(Color.class,
-                    fieldWriter("rgb", Color::getRGB)
+                    fieldWriter("r", Color::getRed),
+                    fieldWriter("g", Color::getGreen),
+                    fieldWriter("b", Color::getBlue),
+                    fieldWriter("alpha", Color::getAlpha)
             );
         }
 

fastjson1-compatible/src/test/java/com/alibaba/fastjson/v2issues/Issue2739.java

@@ -0,0 +1,19 @@
+package com.alibaba.fastjson.v2issues;
+
+import com.alibaba.fastjson.JSON;
+import org.junit.jupiter.api.Test;
+
+import java.awt.*;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class Issue2739 {
+    @Test
+    public void test() {
+        Color blue = Color.BLUE;
+        String colorStr = JSON.toJSONString(blue);
+        assertEquals("{\"r\":0,\"g\":0,\"b\":255,\"alpha\":255}", colorStr);
+        Color color = JSON.parseObject(colorStr, Color.class);
+        assertEquals(blue, color);
+    }
+}