or the iron carbonitride has a mass percentage of about 20 to about 40 when the transition layer 15 includes titanium carbonitride and aluminum carbonitride the titanium carbonitride has a mass percentage of about 80 and the aluminum carbonitride has a mass percentage of about 20 when the transition layer 15 includes titanium carbonitride and chromium carbonitride the titanium carbonitride has a mass percentage of about 65 and the chromium carbonitride has a mass percentage of about 35 when the transition layer 15 includes titanium carbonitride and iron carbonitride the titanium carbonitride has a mass percentage of about 70 and the iron carbonitride has a mass percentage of about 30 the transition layer 15 has a thickness ranging from about 1 u03bcm to about 4 u03bcm the transition layer 15 has a high hardness which enhances the hardness of the housing 10 the color layer 17 is a titanium chromium aluminum layer in the color layer 17 the titanium has a mass percentage of about 10 to about 15 the chromium has a mass percentage of about 20 to about 35 and the aluminum has a mass percentage of about 50 to about 70 in a first exemplary embodiment the titanium has a mass percentage of about 15 the chromium has a mass percentage of about 25 and the aluminum has a mass percentage of about 60 in a second exemplary embodiment the titanium has a mass.