wufyi does transfer the solar / UV data over to pwsweather, but you are right, it is not displayed on their interface.
As far as I know @franz can't get access to data as well, he talks about it here (link). Maybe that has since changed.
UV is an "index" calculated by WU, it is their guess how likely you are to get a sunburn I've seen formulas around the net for that calculation, not sure if they will match WU exactly.
Wufyi will support CWOP stations shortly so your solar data will be used sooner, rather then later.
As far as coloring on API output, it is done by jsonblob.com for easier differential between strings (green) and numerical values (red).