https://www.cnet.com/news/hurricane-harvey-new-colors-national-weather-service-maps-texas-louisiana-tropical-storm-harvey/

In a tweet sent Monday, the NWS explained that so much rain has fallen on Texas and Louisiana because of the storm, the previous map code didn't cover it. Water levels could reach 50 inches in some areas, the NWS reports.

"The tremendous rainfall in Texas is literally and figuratively off the map," an NWS spokesman told CNET.  "In the original map, the top interval for the observed rainfall (marked dark purple) was for amounts of 15 inches and greater, with no upper limit. With Harvey, the updated map is more specific in showing the graphical depiction of rainfall intervals, which aren't often observed at such high levels."