// JavaScript Document 
            var TotalPairCount = 2;
            var CurrPairNo = 1;
            var PrevPairNo = 1;
            
            function Next() { 
                PrevPairNo = CurrPairNo;
                if (CurrPairNo < TotalPairCount) CurrPairNo++;
                // else CurrPairNo = 1;  // uncomment to loop back to first pair
                Swap();
            }
            function Prev() {
                PrevPairNo = CurrPairNo;
                if (CurrPairNo > 1) CurrPairNo--;
                // else CurrPairNo = TotalPairCount;
                Swap();
            }
            function Swap() {
                document.getElementById('ColorSet'+PrevPairNo).style.display = 'none';
                document.getElementById('ColorSet'+CurrPairNo).style.display = '';
            }