diff --git a/history/005_letter_test/src/main/java/com/github/drinkjava2/frog/util/ColorUtils.java b/history/005_letter_test/src/main/java/com/github/drinkjava2/frog/util/ColorUtils.java
new file mode 100644
index 0000000..46e30db
--- /dev/null
+++ b/history/005_letter_test/src/main/java/com/github/drinkjava2/frog/util/ColorUtils.java
@@ -0,0 +1,70 @@
+/* Copyright 2018-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by
+ * applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS
+ * OF ANY KIND, either express or implied. See the License for the specific
+ * language governing permissions and limitations under the License.
+ */
+package com.github.drinkjava2.frog.util;
+
+import java.awt.Color;
+
+/**
+ * Color Utilities used in this project
+ * 
+ * @author Yong Zhu
+ * @since 1.0
+ */
+public class ColorUtils {
+	public static final int RED = 0;
+	public static final int ORANGE = 1;
+	public static final int YELLOW = 2;
+	public static final int GREEN = 3;
+	public static final int CYAN = 4;
+	public static final int BLUE = 5;
+	public static final int MAGENTA = 6;
+	public static final int GRAY = 7;
+
+	private static final Color[] rainbow = new Color[] { Color.RED, Color.ORANGE, Color.YELLOW, Color.GREEN, Color.CYAN,
+			Color.BLUE, Color.MAGENTA,Color.GRAY };
+
+	private static int nextColor = 0;
+
+	private ColorUtils() {// default private constr
+	}
+
+	public static int nextColorCode() {
+		return nextColor++;
+	}
+
+	public static Color nextRainbowColor() {// 返回下一个彩虹色
+		if (nextColor == rainbow.length)
+			nextColor = 0;
+		return rainbow[nextColor++];
+	}
+
+	public static Color colorByCode(int i) {// 数值取模后返回一个固定彩虹色
+		return rainbow[i % rainbow.length];
+	}
+
+	public static Color rainbowColor(float i) { // 根据数值大小范围，在8种彩虹色中取值
+		if (i == 0)
+			return Color.BLACK;
+		if (i == 1)
+			return Color.RED;
+		if (i <= 3)
+			return Color.ORANGE;
+		if (i <= 10)
+			return Color.YELLOW;
+		if (i <= 20)
+			return Color.GREEN;
+		if (i <= 50)
+			return Color.CYAN;
+		if (i <= 100)
+			return Color.BLUE;
+		return Color.MAGENTA;
+	}
+}