Textbox displays Default Value (TextBoxWatermark)

To display the one value within the textbox. And  while enter any text the default value is cleared and my text only displayed it.

<div>
        <asp:TextBox ID="TextBox1" runat="server" Text="Enter PIN"
        onfocus="if(this.value==this.defaultValue) this .value='';" ForeColor="#989898" onblur="if(this.value.length<=0) this.value=this.defaultValue "  ></asp:TextBox>
    </div>