how to access a custom editor's public variables?

I have done this before, but I can't find it again. I have a custom editor class, and I want to set the variables of the editor.

For example, check out killTex in the code below- this is a texture of a little red X that I use as an in-editor delete button (screenshot further below).

I can not for the life of me find out where I assigned that image to killTex. If I wanted, eg, to make it a green checkmark instead, where would I look for the linkage?

 class NodeEditor extends Editor {
 
     // this stuff makes the node deletion button pretty
     var killTex:Texture;
     var nullStyle:GUIStyle = new GUIStyle();
     var bDim:int = 20;
     var ScreenHeightCorrection:int = 38; //the fuck?
 
     protected function deleteButton (pos:Vector3) :boolean {
         pos = target.transform.TransformPoint( pos );
 
         var bPos:Vector3 = sceneCam.WorldToScreenPoint(pos);
         bPos.y = Screen.height - bPos.y - ScreenHeightCorrection;
         bPos.y -= bDim + 2;
         bPos.x += 2;
 
         Handles.BeginGUI();            
         var del:boolean = GUI.Button( Rect(bPos.x, bPos.y, bDim, bDim), killTex, nullStyle );
         Handles.EndGUI();
 
         return del;
     }
 
 
 
     // note: SceneView is undocumented. If at any time in the future it breaks, we will all die horribly.
     function get sceneCam () :Camera {
         return SceneView.lastActiveSceneView.camera;
     }
 
 
     function OnInspectorGUI () {
         DrawDefaultInspector();
     }
 
     function get owner () :NodeList {
         return (target as NodeList);
     }
 }