Black_Star,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.block{
width: 150px;
height: 150px;
}
.one{
background-color: rgb(255, 250, 44);
}
.two{
background-color: rgb(5, 250, 44);
}
.three{
background-color: rgb(25, 250, 144);
}
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
function fn(num)
{
return num < 0 ? 0 : num > 255 ? 255 : num
}
$("div").each(function(indx, el){
let color = $(el).css("backgroundColor"),
[r,g,b] = color.match(/\d+/g);
r -= 200;
g -= 100;
b = +b + 70;
$(this).text(color +'\nrgb('+[r,g,b].map(fn)+')' )
});
});
</script>
</head>
<body>
<div class="block one"></div>
<div class="block two"></div>
<div class="block three"></div>
</body>
</html>