to use colors in WPF, you can do this:
txbName.BorderBrush = (SolidColorBrush)(new BrushConverter().ConvertFrom("#00b4d8"));
//-- OR
txbName.BorderBrush = new SolidColorBrush(Color.FromRgb(255, 0, 128));
This way, you should be able to use both Hex and RGB colors :)