Add legends in your .aspx file. The charting control will take care of bar color for legends.
<asp:chart id="Chart1" runat="server" BackColor="OrangeRed" Width="600px"
Height="300px" BorderColor="26, 59, 105" Palette="BrightPastel"
BorderDashStyle="Solid" BackSecondaryColor="White"
BackGradientStyle="TopBottom" BorderWidth="2"
ImageLocation="~/TempImages/ChartPic_#SEQ(300,3)"
BackImageTransparentColor="White">
<titles>
<asp:Title ShadowColor="32, 0, 0, 0" Font="Trebuchet MS, 14.25pt, style=Bold" ShadowOffset="3" Text="Attendance" ForeColor="26, 59, 105"></asp:Title>
</titles>
<legends>
<asp:Legend Enabled="True" IsTextAutoFit="False" Name="Default" BackColor="Transparent" Font="Trebuchet MS, 8.25pt, style=Bold" Docking="Bottom"></asp:Legend>
</legends>
<borderskin SkinStyle="Emboss"></borderskin>
<series>
<asp:Series IsValueShownAsLabel="True" ChartArea="ChartArea1" Name="Default" CustomProperties="LabelStyle=Bottom" BorderColor="180, 26, 59, 105" LabelFormat="#.#,H"></asp:Series>
<asp:Series IsValueShownAsLabel="True" ChartArea="ChartArea1" Name="Default1" CustomProperties="LabelStyle=Bottom" BorderColor="180, 26, 59, 105" LabelFormat="#.#,H"></asp:Series>
<asp:Series IsValueShownAsLabel="True" ChartArea="ChartArea1" Name="Default2" CustomProperties="LabelStyle=Bottom" BorderColor="180, 26, 59, 105" LabelFormat="#.#,H"></asp:Series>
</series>
<chartareas>
<asp:ChartArea Name="ChartArea1" BorderColor="64, 64, 64, 64" BorderDashStyle="Solid" BackSecondaryColor="White" BackColor="64, 165, 191, 228" ShadowColor="Transparent" BackGradientStyle="TopBottom">
<axisy2 Enabled="False"></axisy2>
<axisx2 Enabled="False"></axisx2>
<area3dstyle Rotation="10" Perspective="10" Inclination="15" IsRightAngleAxes="False" WallWidth="0" IsClustered="False" />
<axisy LineColor="64, 64, 64, 64" IsLabelAutoFit="False" ArrowStyle="Triangle">
<LabelStyle Font="Trebuchet MS, 8.25pt, style=Bold" Format="#.#,H" />
<MajorGrid LineColor="64, 64, 64, 64" />
</axisy>
<axisx LineColor="64, 64, 64, 64" IsLabelAutoFit="False" ArrowStyle="Triangle">
<LabelStyle Font="Trebuchet MS, 8.25pt, style=Bold" IsStaggered="false" />
<MajorGrid LineColor="64, 64, 64, 64" />
</axisx>
</asp:ChartArea>
</chartareas>
</asp:chart>
notice in the above example
<legends>
<asp:Legend Enabled="True" IsTextAutoFit="False" Name="Default" BackColor="Transparent" Font="Trebuchet MS, 8.25pt, style=Bold" Docking="Bottom"></asp:Legend>
</legends>