你使用一个额外的属性;fill-opacity:该属性接受一个介于0.0到1.0之间的十进制数;其中0.0是完全透明的。

例如:

<rect ... fill="#044B94" fill-opacity="0.4"/>

此外，你有以下:

描边的描边不透明度属性 整个对象的不透明度

作为一个尚未完全标准化的解决方案(尽管与CSS3中的颜色语法一致)，你可以使用例如fill="rgba(124,240,10,0.5)"。在Firefox, Opera, Chrome中工作良好。

举个例子。

fill="#044B9466"

这是SVG中十六进制符号的RGBA颜色，用十六进制值定义。这是有效的，但不是所有程序都能正确显示它…

您可以在这里找到对该语法的浏览器支持:https://caniuse.com/#feat=css-rrggbbaa

截至2017年8月:RGBA填充颜色将在Mozilla Firefox (54)， Apple Safari(10.1)和Mac OS X Finder的“快速视图”上正常显示。然而，谷歌Chrome直到62版才支持此语法(之前由54版支持，实验平台功能标志启用)。

截至2021年4月，Inkscape版本1.0.2无法在SVG文件中读取这种格式，而是将任何RGBA颜色转换为不透明的黑色。错误报告在这里:https://gitlab.com/inkscape/inbox/-/issues/1195

在SVG元素中使用fill-opacity属性。

默认值为1，最小值为0，在步进中使用十进制值EX: 0.5 = alpha的50%。注意:有必要定义填充颜色来应用填充不透明度。

请看我的例子。

参考文献

要使填充完全透明，fill="transparent"在现代浏览器中似乎是有效的。但它在微软Word (Mac版)中不起作用，我不得不使用fill-opacity="0"。

更新

根据下面Alex Henrie的评论，fill="none"可能是更好的选择。

To change transparency on an svg code the simplest way is to open it on any text editor and look for the style attributes. It depends on the svg creator the way the styles are displayed. As i am an Inkscape user the usual way it set the style values is through a style tag just as if it were html but using svg native attributes like fill, stroke, stroke-width, opacity and so on. opacity affects the whole svg object, or path or group in which its stated and fill-opacity, stroke-opacity will affect just the fill and the stroke transparency. That said, I have also used and tasted to just use fill and instead of using#fff use instead the rgba standard like this rgba(255, 255, 255, 1) just as in css. This works fine for must modern browsers.

请记住，如果您打算进一步重新编辑svg，根据我的经验，最好的做法是始终保持一个原始版本在手边。Inkscape在手动修改svg方面更加灵活，但Illustrator和CorelDraw可能会在导入和编辑svg方面存在问题。

例子

<path style="fill:#ff0000;fill-opacity:1;stroke:#1a1a1a;stroke-width:2px;stroke-opacity:1" d="m 144.44226,461.14425 q 16.3125,-15.05769 37.64423,-15.05769 21.33173,0 36.38942,15.05769 15.0577,15.05769 15.0577,36.38942 0,21.33173 -15.0577,36.38943 -15.05769,16.3125 -36.38942,16.3125 -21.33173,0 -37.64423,-16.3125 -15.05769,-15.0577 -15.05769,-36.38943 0,-21.33173 15.05769,-36.38942 z M 28.99995,35.764435 l 85.32692,0 23.84135,52.701923 386.48078,0 q 10.03846,0 17.5673,7.528847 8.78366,7.528845 8.78366,17.567305 0,7.52885 -2.50962,12.54808 l -94.11058,161.87019 q -13.80288,27.60577 -45.17307,27.60577 l -194.4952,0 -26.35096,40.15385 q -2.50962,6.27404 -2.50962,7.52885 0,6.27404 6.27404,6.27404 l 298.64424,0 0,50.1923 -304.91828,0 q -25.09615,0 -41.40865,-13.80288 -15.05769,-13.80289 -15.05769,-38.89904 0,-15.05769 6.27404,-25.09615 l 38.89903,-63.9952 -92.855766,-189.475962 -52.701924,0 0,-52.701923 z M 401.67784,461.14425 q 15.05769,-15.05769 36.38942,-15.05769 21.33174,0 36.38943,15.05769 16.3125,15.05769 16.3125,36.38942 0,21.33173 -16.3125,36.38943 -15.05769,16.3125 -36.38943,16.3125 -21.33173,0 -36.38942,-16.3125 -15.05769,-15.0577 -15.05769,-36.38943 0,-21.33173 15.05769,-36.38942 z"/>

示例2

<path style="fill:#ff0000;fill-opacity:.5;stroke:#1a1a1a;stroke-width:2px;stroke-opacity:1" d="m 144.44226,461.14425 q 16.3125,-15.05769 37.64423,-15.05769 21.33173,0 36.38942,15.05769 15.0577,15.05769 15.0577,36.38942 0,21.33173 -15.0577,36.38943 -15.05769,16.3125 -36.38942,16.3125 -21.33173,0 -37.64423,-16.3125 -15.05769,-15.0577 -15.05769,-36.38943 0,-21.33173 15.05769,-36.38942 z M 28.99995,35.764435 l 85.32692,0 23.84135,52.701923 386.48078,0 q 10.03846,0 17.5673,7.528847 8.78366,7.528845 8.78366,17.567305 0,7.52885 -2.50962,12.54808 l -94.11058,161.87019 q -13.80288,27.60577 -45.17307,27.60577 l -194.4952,0 -26.35096,40.15385 q -2.50962,6.27404 -2.50962,7.52885 0,6.27404 6.27404,6.27404 l 298.64424,0 0,50.1923 -304.91828,0 q -25.09615,0 -41.40865,-13.80288 -15.05769,-13.80289 -15.05769,-38.89904 0,-15.05769 6.27404,-25.09615 l 38.89903,-63.9952 -92.855766,-189.475962 -52.701924,0 0,-52.701923 z M 401.67784,461.14425 q 15.05769,-15.05769 36.38942,-15.05769 21.33174,0 36.38943,15.05769 16.3125,15.05769 16.3125,36.38942 0,21.33173 -16.3125,36.38943 -15.05769,16.3125 -36.38943,16.3125 -21.33173,0 -36.38942,-16.3125 -15.05769,-15.0577 -15.05769,-36.38943 0,-21.33173 15.05769,-36.38942 z"/>

示例3

<path style="fill:rgba(255, 0, 0, .5);stroke:rgba(242, 242, 242, .5);stroke-width:2px" d="m 144.44226,461.14425 q 16.3125,-15.05769 37.64423,-15.05769 21.33173,0 36.38942,15.05769 15.0577,15.05769 15.0577,36.38942 0,21.33173 -15.0577,36.38943 -15.05769,16.3125 -36.38942,16.3125 -21.33173,0 -37.64423,-16.3125 -15.05769,-15.0577 -15.05769,-36.38943 0,-21.33173 15.05769,-36.38942 z M 28.99995,35.764435 l 85.32692,0 23.84135,52.701923 386.48078,0 q 10.03846,0 17.5673,7.528847 8.78366,7.528845 8.78366,17.567305 0,7.52885 -2.50962,12.54808 l -94.11058,161.87019 q -13.80288,27.60577 -45.17307,27.60577 l -194.4952,0 -26.35096,40.15385 q -2.50962,6.27404 -2.50962,7.52885 0,6.27404 6.27404,6.27404 l 298.64424,0 0,50.1923 -304.91828,0 q -25.09615,0 -41.40865,-13.80288 -15.05769,-13.80289 -15.05769,-38.89904 0,-15.05769 6.27404,-25.09615 l 38.89903,-63.9952 -92.855766,-189.475962 -52.701924,0 0,-52.701923 z M 401.67784,461.14425 q 15.05769,-15.05769 36.38942,-15.05769 21.33174,0 36.38943,15.05769 16.3125,15.05769 16.3125,36.38942 0,21.33173 -16.3125,36.38943 -15.05769,16.3125 -36.38943,16.3125 -21.33173,0 -36.38942,-16.3125 -15.05769,-15.0577 -15.05769,-36.38943 0,-21.33173 15.05769,-36.38942 z"/>

请注意，在最后一个例子中，填充不透明度和笔画不透明度已经被删除，因为rgba标准在这两种情况下都覆盖了颜色和alpha通道。

我分享一个相关的技巧，当你想让SVG继承容器的样式，如正常状态，悬停状态和访问状态时，你可能会遇到: 在路径上使用fill='currentColor'。这就是SVG是如何产生的字体awesome图标可以采取任何前色应用到字体!