Html code for adding map
    
        <div id="map" style="height:480px; width:360px;"></div>

    css for loading map
    .leaflet-div-icon
{
    background-image: url('http://cloudmade.com/images/layout/cm-logo.png');
}
    
    Logic for changing marker colour
    
        var map = L.map('map').setView([51.5, -0.09], 13);
    
    L.marker([51.49, -0.09]).addTo(map)
        .bindPopup('Demo CSS3 popup. <br> Easily customizable.');
    
    const myCustomColour = '#5f93ed'
    
    const markerHtmlStyles = `
      background-color: ${myCustomColour};
      width: 15px;
      height: 15px;
      font-size:15px;
      text-align:center;
      display: block; 
      `
    
    function thing(ct) {
        return L.divIcon({
            className: "box",
            iconAnchor: [12, 25],
            labelAnchor: [-6, 0],
            popupAnchor: [0, -15],
            html: `<span style="${markerHtmlStyles}" >M</span>`
        })
    }
    
    L.marker([51.51, -0.09], {
            icon: thing("hello")
        }).addTo(map)
        .bindPopup('divIcon CSS3 popup. <br> Supposed to be easily stylable.');

Html code for adding map

<div id="map" style="height:480px; width:360px;"></div>

css for loading map

.leaflet-div-icon
{
    background-image: url('http://cloudmade.com/images/layout/cm-logo.png');
}

Logic for changing marker colour

var map = L.map('map').setView([51.5, -0.09], 13);
        
L.marker([51.49, -0.09]).addTo(map)
    .bindPopup('Demo CSS3 popup. <br> Easily customizable.');
        
const myCustomColour = '#5f93ed'
        
const markerHtmlStyles = `
    background-color: ${myCustomColour};
    width: 15px;
    height: 15px;
    font-size:15px;
    text-align:center;
    display: block; 
`
        
function thing(ct) {
    return L.divIcon({
        className: "box",
        iconAnchor: [12, 25],
        labelAnchor: [-6, 0],
        popupAnchor: [0, -15],
        html: `<span style="${markerHtmlStyles}" >M</span>`
    })
}
       
L.marker([51.51, -0.09], {
    icon: thing("hello")
}).addTo(map)
    .bindPopup('divIcon CSS3 popup. <br> Supposed to be easily stylable.');