change svg code for color background
<svg width="100%" height="100%">
<defs>
<filter x="0" y="0" width="1" height="1" id="solid">
<feFlood flood-color="yellow"/>
<feComposite in="SourceGraphic"/>
</filter>
</defs>
<text filter="url(#solid)" x="20" y="50" font-size="50">solid background</text>
</svg>
See: https://stackoverflow.com/questions/15500894/background-color-of-text-in-svg