JSFiddle - React, Tailwind, and code Playground

HTML

Setting the BODY's background to the average color in the following image:

<br/><br/>
<p class="imagecolor">
one this should be blue
</p>
<p class="imagecolor">
one this should be light brown
</p>
<p class="imagecolor">
one this should be red
</p class="imagecolor">


<img id="i" class="image"...

JavaScript

var r = document.getElementsByClassName('image');
    var targets = document.getElementsByClassName('imagecolor');
    var rgb = [];
    for (p = 0 ; p < r.length ; p++ ){
       rgb.push(getAverageRGB(r[p]));
    }
    rgb.forEach((el,i) => {
       targets[i].style.color = 'rgb('+el.r+','+el.g+','+el.b+')';
    })
    

function getAverageRGB(imgEl) {
    
    var blockSize = 5, // only visit every 5 pixels
        defaultRGB = {r:0,g:0,b:0}, // for non-supporting envs
        canvas = document.createElement('canvas'),
        context = canvas.getContext && canvas.getContext('2d'),
        data, width, height,
        i = -4,
        length,
        rgb = {r:0,g:0,b:0},
        count = 0;
        
    if (!context) {
        return defaultRGB;
    }
    
    height = canvas.height = imgEl.naturalHeight || imgEl.offsetHeight || imgEl.height;
    width = canvas.width = imgEl.naturalWidth || imgEl.offsetWidth || imgEl.width;
    
    context.drawImage(imgEl, 0, 0);
    
    try {
        data = context.getImageData(0, 0, width, height);
    } catch(e) {
        /* security error, img on diff domain */alert('x');
        return defaultRGB;
    }
    
    length = data.data.length;
    
    while ( (i += blockSize * 4) < length ) {
        ++count;
        rgb.r += data.data[i];
        rgb.g += data.data[i+1];
        rgb.b += data.data[i+2];
    }
    
    // ~~ used to floor values
    rgb.r = ~~(rgb.r/count);
    rgb.g = ~~(rgb.g/count);
    rgb.b = ~~(rgb.b/count);
    
    return rgb;
    
}