Use RGB color to fill Rectangle
<Window x:Class="WpfApplication1.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="WrapPanel" Height="300" Width="300"> <WrapPanel Background="AliceBlue"> <Rectangle Fill="#FF000000" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FF111111" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FF222222" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FF333333" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FF444444" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FF555555" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FF666666" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FF777777" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FF888888" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FF999999" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FFAAAAAA" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FFBBBBBB" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FFCCCCCC" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FFDDDDDD" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FFEEEEEE" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> <Rectangle Fill="#FFFFFFFF" Height="50" Width="50" Stroke="Black" RadiusX="10" RadiusY="10" /> </WrapPanel> </Window>