Click here for a table containing the FIPS codes for all counties.
You will need a color legend. You can use an image editor such as inkspace or adobe illustrator. Alternatively, you can add a colorbar by adding some code to the svg file.
<svg xmlns="http://www.w3.org/2000/svg" height="600" width="1400">
<defs>
<linearGradient id="grad1" x1="0%" y1="0%" x2="0%" y2="100%">
<stop offset="0%" style="stop-color:#009800;stop-opacity:1" />
<stop offset="100%" style="stop-color:0d0d0d;stop-opacity:1" />
</linearGradient>
</defs>
<rect x="1000" y="100" width="50" height="500" style="stroke-width:3;stroke:rgb(0,0,0)" fill="url(#grad1)"/>
</svg>