document.querySelectorAll('.test > div').forEach( elem => {
console.log( 'formatted as', getComputedStyle(elem)['background-color'] );
} );
.named-color { background-color: magenta; }
.currentcolor { background-color: currentColor; }
.no-alpha-hex { background-color: #FF00FF; }
.no-alpha-rgb { background-color: rgb(255,0,255); }
.no-alpha-rgb-perc { background-color: rgb(100%,0%,100%); }
.no-alpha-hsl { background-color: hsl(300deg, 100%, 50%); }
.no-alpha-rgba { background-color: rgb(255,0,255,1); }
.no-alpha-rgba-perc { background-color: rgb(100%,0%,100%,1); }
.no-alpha-hsla { background-color: hsl(300deg, 100%, 50%,1); }
.alpha-hex { background-color: #FF00FF80; }
.alpha-rgba { background-color: rgba(255,0,255,0.5); }
.alpha-rgba-perc { background-color: rgba(100%,0%,100%,0.5); }
.alpha-hsla { background-color: hsla(300deg, 100%, 50%,0.5); }
.test { color: magenta; }
.test > div {
width: 100%;
height: 5px;
}
<div class="test">
<div class="named-color"></div>
<div class="currentcolor"></div>
<div class="no-alpha-hex"></div>
<div class="no-alpha-rgb"></div>
<div class="no-alpha-rgb-perc"></div>
<div class="no-alpha-hsl"></div>
<div class="no-alpha-rgba"></div>
<div class="no-alpha-rgba-perc"></div>
<div class="no-alpha-hsla"></div>
<div class="alpha-hex"></div>
<div class="alpha-rgba"></div>
<div class="alpha-rgba-perc"></div>
<div class="alpha-hsla"></div>
</div>