gistfile1.scala

Works:
class Marker private (val color:String){
  override def toString():String = "marker color " + color

}

object Marker {
  private val markers = Map(
    "red" -> new Marker("red"),
    "blue" -> new Marker("blue"),  
    "green" -> new Marker("green")
  )

  def withColor(color:String)=
    if(markers.contains(color)) markers(color) else new Marker("green")
}

Doesn't:
class Marker private (val color:String){
  override def toString():String = "marker color " + color

}

object Marker {
  private val markers = Map(
    "red" -> new Marker("red"),
    "blue" -> new Marker("blue"),  
    "green" -> new Marker("green")
  )

  def withColor(color:String){
    if(markers.contains(color)) markers(color) else new Marker("green")
  }

}