html - How to modify the fill color of an SVG image when being served as background image?

Question

Placing the SVG output directly inline with the page code I am able to simply modify fill colors with CSS like so:

polygon.mystar {
    fill: blue;
}?

circle.mycircle {
    fill: green;
}

This works great, however I'm looking for a way to modify the "fill" attribute of an SVG when it's being served as a BACKGROUND-IMAGE.

html {      
    background-image: url(../img/bg.svg);
}

How can I change the colors now? Is it even possible?

For reference, here are the contents of my external SVG file:

<svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
     width="320px" height="100px" viewBox="0 0 320 100" enable-background="new 0 0 320 100" xml:space="preserve">
<polygon class="mystar" fill="#3CB54A" points="134.973,14.204 143.295,31.066 161.903,33.77 148.438,46.896 151.617,65.43 134.973,56.679 
    118.329,65.43 121.507,46.896 108.042,33.77 126.65,31.066 "/>
<circle class="mycircle" fill="#ED1F24" cx="202.028" cy="58.342" r="12.26"/>
</svg>

Answer 1

I needed something similar and wanted to stick with CSS. Here are LESS and SCSS mixins as well as plain CSS that can help you with this. Unfortunately, it's browser support is a bit lax. See below for details on browser support.

LESS mixin:

.element-color(@color) {
  background-image: url('data:image/svg+xml;utf8,<svg ...><g stroke="@{color}" ... /></g></svg>');
}

LESS usage:

.element-color(#fff);

---

SCSS mixin:

@mixin element-color($color) {
  background-image: url('data:image/svg+xml;utf8,<svg ...><g stroke="#{$color}" ... /></g></svg>');
}

SCSS usage:

@include element-color(#fff);

---

CSS:

// color: red
background-image: url('data:image/svg+xml;utf8,<svg ...><g stroke="red" ... /></g></svg>');

---

Here is more info on embedding the full SVG code into your CSS file. It also mentioned browser compatibility which is a bit too small for this to be a viable option.