System.Drawing.Color

KnownColor selectedColor = (KnownColor)System.Enum.Parse(typeof(KnownColor), rmLanguage.GetString("tabPage1.BackColor"));

tabPage1.BackColor = System.Drawing.Color.FromKnownColor(selectedColor);

I think with KnownColor and System.Drawing.Color.FromKnownColor you can get the value from resource and can set it to your tabpage control. Take a look at the below link for info, there's a similar sample code,

http://www.java2s.com/Code/CSharp/2D-Graphics/Listallknowncolorinasystem.htm