Why is this svg not affected by a filter?

Question

This question asks to change the color of an svg using css. I had thought it would be possible to achieve this with a filter, but I'm running into a problem.

I can blur the image with a css filter, but I can't change the color. It seems that from this article, it should be possible to adjust a background-image svg's color using a filter. Where am I going wrong here?

.btn-icon {
  border: 1px solid black;
  height: 40px;
  width: 40px;
  padding: 0px;
  background: url("https://image.flaticon.com/icons/svg/1034/1034153.svg");
  background-size: cover;
}

.blur {
  filter: blur(3px)
}

.color {
  filter: hue-rotate(40deg) saturate(0.5) brightness(390%) saturate(4); 
}

<button class="btn-icon blur"></button>
<button class="btn-icon color"></button>

Answer 1

@Shahar had this right; it's to do with how the svg is put together. Without a fill attribute on the path, it's not possible to use color filters on the image. The raw svg has been added below, with one of the paths having color, the other not.

The filter is applied to the part of the image with the fill attribute only.

.btn-icon {
  border: 1px solid black;
  height: 40px;
  width: 40px;
  padding: 0px;
  background: url("https://image.flaticon.com/icons/svg/1034/1034153.svg");
  background-size: cover;
}

.blur {
  filter: blur(3px)
}

.color {
  filter: hue-rotate(40deg) saturate(0.5) brightness(390%) saturate(4);
 }
 
 #testSvg {
  width: 40px;
   filter: hue-rotate(40deg) saturate(0.5) brightness(390%) saturate(4); 
 }

<button class="btn-icon blur"></button>
<button class="btn-icon color"></button>


<?xml version="1.0" encoding="iso-8859-1"?>
<!-- Generator: Adobe Illustrator 19.0.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
<svg id="testSvg" version="1.1" id="Capa_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
	 viewBox="0 0 511.874 511.874" style="enable-background:new 0 0 511.874 511.874;" xml:space="preserve">
<g>
	<g>
		<g>
			<path fill="red" d="M490.114,12.813H132.568c-12.012,0.014-21.746,9.748-21.76,21.76v98.62l-16.35-24.525
				c-7.484-11.289-22.535-14.676-34.133-7.68l-33.638,20.224c-11.016,6.464-19.097,16.946-22.545,29.244
				c-12.271,44.681-3.166,121.66,109.824,234.667C203.821,474.885,270.816,499.06,316.99,499.06
				c10.69,0.049,21.339-1.34,31.659-4.13c12.293-3.448,22.775-11.518,29.252-22.519l20.198-33.673
				c6.968-11.589,3.584-26.609-7.68-34.091l-80.546-53.692c-11.049-7.308-25.859-4.905-34.031,5.521l-23.45,30.148
				c-2.451,3.226-6.897,4.166-10.445,2.21l-4.463-2.458c-14.686-8.004-32.964-17.971-69.879-54.886
				c-3.994-3.994-7.612-7.731-11.008-11.307h333.517c11.982,0.009,21.713-9.676,21.76-21.658V34.573
				C511.86,22.561,502.126,12.827,490.114,12.813z M229.318,401.362l4.335,2.381c10.897,6.093,24.614,3.266,32.213-6.639
				l23.45-30.148c2.666-3.396,7.49-4.179,11.093-1.801l80.546,53.692c3.659,2.439,4.759,7.321,2.5,11.093l-20.198,33.673
				c-4.218,7.233-11.071,12.553-19.123,14.848c-40.337,11.093-110.933,1.707-218.078-105.446S9.56,195.273,20.627,154.97
				c2.293-8.051,7.61-14.903,14.839-19.123l33.673-20.207c3.773-2.254,8.652-1.155,11.093,2.5l53.717,80.546
				c2.382,3.602,1.599,8.43-1.801,11.093l-30.157,23.458c-9.903,7.597-12.731,21.311-6.639,32.205l2.389,4.335
				c8.533,15.65,19.14,35.123,57.805,73.779C194.212,382.213,213.677,392.828,229.318,401.362z M494.808,298.526
				c-0.028,2.567-2.127,4.627-4.693,4.608H141.203c-11.083-12.674-20.64-26.604-28.476-41.506l-2.458-4.48
				c-1.96-3.54-1.022-7.982,2.202-10.428l30.157-23.458c10.43-8.17,12.833-22.982,5.521-34.031l-20.275-30.43V34.573
				c-0.014-1.249,0.476-2.451,1.359-3.334c0.883-0.883,2.085-1.373,3.334-1.359h357.547c1.249-0.014,2.451,0.476,3.334,1.359
				c0.883,0.883,1.373,2.085,1.359,3.334V298.526z"/>
			<path d="M460.725,52.323l-142.618,108.16c-4.035,2.932-9.499,2.932-13.534,0L162.008,52.323
				c-3.756-2.849-9.111-2.113-11.959,1.643c-2.849,3.756-2.113,9.111,1.643,11.959l142.583,108.151
				c10.144,7.494,23.989,7.494,34.133,0L471.034,65.925c1.805-1.368,2.992-3.398,3.299-5.642c0.307-2.244-0.29-4.518-1.661-6.321
				C469.824,50.213,464.478,49.48,460.725,52.323z"/>
			<path d="M238.517,174.793l-87.415,93.611c-3.214,3.447-3.025,8.848,0.422,12.062c3.447,3.214,8.848,3.025,12.062-0.422
				l87.416-93.653c2.888-3.484,2.553-8.617-0.762-11.698C246.924,171.612,241.78,171.656,238.517,174.793z"/>
			<path d="M384.728,174.793c-3.214-3.447-8.614-3.637-12.062-0.422c-3.447,3.214-3.637,8.614-0.422,12.062l87.39,93.611
				c3.214,3.447,8.614,3.637,12.062,0.422c3.447-3.214,3.637-8.614,0.422-12.062L384.728,174.793z"/>
		</g>
	</g>
</g>
</svg>

Answer 2

You have two main issues:

1. There is a typo. .color: should be .color.
2. Nothing happens if you hue-rotate() a black and white image. You just get the same black and white image. #000000 just becomes #000000. Same for white. The same applies for most of the other CSS filter primitives. The only one that can really add in any colour is the sepia() filter. And it seems you have to jump through quite a few hoops to get useful colour out of it.

Here is an example with a filter set borrowed from another example elsewhere.

.btn-icon {
  border: 1px solid black;
  height: 40px;
  width: 40px;
  padding: 0px;
  background: url("https://image.flaticon.com/icons/svg/1034/1034153.svg");
  background-size: cover;
}

.blur {
  filter: blur(3px)
}

.color {
  filter: invert(100%) grayscale(100%) brightness(40%) sepia(100%) hue-rotate(-50deg) saturate(600%) contrast(0.8);
 }

<button class="btn-icon blur"></button>
<button class="btn-icon color"></button>