每次点击按钮都会使背景色改变

<script language="Javascript">
 <!--
 function backcolor(form){
 
         temp = ""
 
         for (var i = 0; i < 16; i++) {
 
                 temp = form.color[i].value
 
                 if (form.color[i].checked){ document.bgColor = temp }
                 }
          }
 
 function randombackground(){
 
         document.bgColor = getColor()
         }
 function getColor(){
         currentdate = new Date()
         backgroundcolor = currentdate.getSeconds()
         if (backgroundcolor > 44)
                 backgroundcolor = backgroundcolor - 45
         else if (backgroundcolor > 29)
                 backgroundcolor = backgroundcolor - 30
         else if (backgroundcolor > 15)
                 backgroundcolor = backgroundcolor - 16
         if (backgroundcolor == 0 )
                 return "olive";
         else if (backgroundcolor == 1 )
                 return "teal";
         else if (backgroundcolor == 2 )
                 return "red";
         else if (backgroundcolor == 3 )
                 return "blue";
         else if (backgroundcolor == 4 )
                 return "maroon";
         else if (backgroundcolor == 5 )
                 return "navy";
         else if (backgroundcolor == 6 )
                 return "lime";
         else if (backgroundcolor == 7 )
                 return "fuschia";
         else if (backgroundcolor == 8 )
                 return "green";
         else if (backgroundcolor == 9 )
                 return "purple";
         else if (backgroundcolor == 10 )
                 return "gray";
         else if (backgroundcolor == 11 )
                 return "yellow";
         else if (backgroundcolor == 12 )
                 return "aqua";
         else if (backgroundcolor == 13 )
                 return "black";
         else if (backgroundcolor == 14 )
                 return "white";
         else if (backgroundcolor == 15 )
                 return "silver";
         }
 
 // -->
 </script>