because your flag get reset when you recall, move it out of function:
var click=0;
function farbe1(){
var stern_style = document.getElementById('kugel1').style;
if(click != 0){
stern_style.setProperty('fill','#F57200');
click = 0;
}
else if(click == 0){
stern_style.setProperty('fill','red');
click = 1;
}
}