diff --git a/src/demo/parallel/Complex.java b/src/demo/parallel/Complex.java
index 134a37946..04b8ce091 100644
--- a/src/demo/parallel/Complex.java
+++ b/src/demo/parallel/Complex.java
@@ -71,6 +71,25 @@ public Complex plus(Complex b) {
         return this;
     }
 
+    /**
+     * Subtract operation.
+     * @param b minuend
+     * @return this Complex object whose value is (this - b)
+     */
+    public Complex minus(Complex b) {
+        re -= b.re;
+        im -= b.im;
+        return this;
+    }
+
+    public double getRe() {
+        return re;
+    }
+
+    public double getIm() {
+        return im;
+    }
+
     /**
      * Multiply operation.
      * @param  b multiplier
diff --git a/src/demo/parallel/MandelbrotSetTask.java b/src/demo/parallel/MandelbrotSetTask.java
index adbb217b8..a09078d63 100644
--- a/src/demo/parallel/MandelbrotSetTask.java
+++ b/src/demo/parallel/MandelbrotSetTask.java
@@ -273,9 +273,9 @@ protected Long call() throws Exception {
      */
     private int calc(Complex comp) {
         int count = 0;
-        Complex c = new Complex(0, 0);
+        Complex c = new Complex(0.308, 0);
         do {
-            c = c.times(c).plus(comp);
+            c = c.times(c).minus(comp);
             count++;
         } while (count < CAL_MAX_COUNT && c.lengthSQ() < LENGTH_BOUNDARY);
         return count;
@@ -351,20 +351,20 @@ private Color getColor(int count) {
          * Color stops for colors table: color values
          */
         Color[] cc = {
-            Color.rgb(40, 0, 0),
+            Color.VIOLET,
             Color.RED,
             Color.WHITE,
-            Color.RED,
-            Color.rgb(100, 0, 0),
-            Color.RED,
-            Color.rgb(50, 0, 0)
+            Color.CYAN,
+            Color.PURPLE,
+            Color.HOTPINK,
+            Color.MISTYROSE
         };
         
         /**
          * Color stops for colors table: relative position in the table
          */
         double[] cp = {
-            0, 0.17, 0.25, 0.30, 0.5, 0.75, 1,};
+            0, 0.10, 0.20, 0.30, 0.5, 0.70, 1,};
         
         /**
          * Color table population
diff --git a/src/test/demo/parallel/ComplexTest.java b/src/test/demo/parallel/ComplexTest.java
new file mode 100644
index 000000000..20278f2a4
--- /dev/null
+++ b/src/test/demo/parallel/ComplexTest.java
@@ -0,0 +1,19 @@
+package test.demo.parallel;
+
+import demo.parallel.Complex;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ComplexTest {
+
+    @Test
+    public void subtractTest() {
+        Complex a = new Complex(7.0, 2.0);
+        Complex b = new Complex(3.0, 1.0);
+        Complex difference = a.minus(b);
+
+        assertEquals(4.0, difference.getRe(), 1e-10, "Real part must be 4.0" );
+        assertEquals(1.0, difference.getIm(), 1e-10, "Imaginary part must be 1.0");
+    }
+}