var opacity = 0.2;
$(".article-block:not(#article-featured)").each(function() {
    var c1 = $(this).css('border-top-color');
    c=c1.substring(c1.indexOf('(') + 1, c1.lastIndexOf(')')).split(/,\s*/),r=c[0],g=c[1],b=c[2];
    $(this).css('background', 'rgba('+r+','+g+','+b+','+opacity+')');
});