How to hide tooltip background image

I have problem in unity. I make a tooltip with background image. When the mouse hover, tooltip text and tooltip background image is appear. But when the mouse out, only tooltip text disappear and tooltip background image is not disappear. I want to disappear tooltip background image. How to make it? Please help me.

if(GUI.Button(Rect( 0 ,(Screen.height/4)*3, Screen.width/14 ,Screen.height/4 ), GUIContent(“ヒント”,“折り 目ガイ ド をなぞっ てみまし ょ う”),hintStyle)){
showToolTip=true;
};
if(showToolTip){
GUI.Label(Rect (Screen.width/13,(Screen.height/4)*3.5, Screen.width/3, 50), GUI.tooltip, tooltipStyle);
}