Help with coloring a button?

I'm trying to make a plain GUI button that is blue, with no text on it. Here is my code,

     var btnTexture : Texture;
     var btn_Color : Color.blue;
     function OnGUI() {
         if (!btnTexture) {
             Debug.LogError("Please assign a texture on the inspector");
             return;
         }
         GUI.Color = Color.blue;
         if (GUI.Button(Rect(10,70,50,50),btnTexture))
             Debug.Log("Clicked the button with an image");
         if (GUI.Button(Rect(10,10,100,30),"Test"))
             Debug.Log("Clicked the button with text");
     }

Unity says that "The color blue does not denote a valid type."

I'm going to have multiple colored buttons in this script. Red, orange, yellow, green, blue, and purple. Is there a way I can make it so each button has a different color? Also, how do I even make the button have color because Unity makes an error.