...
<svg ...>
<defs>
<path id="..." d="..." />
<polyon id="..." points="..." />
</defs>
...
<use xlink:href="#id" ....? />
</svg>
The xlink:href attribute will lookup any graphic in the defs section with the given id and embed this in the <use/> element, which can contain transforms, fill and stroke definitions that can be manipulated in other ways at the same time. So by putting the "fill" attributes in the <use/> element, it should be possible to apply both a color and symboId from a ThresholdWarningLevel at the same time.
...