As of December 2013, the tracts marked in red had fixed fast Internet connections (DSL or cable modem) reported for fewer than 20% of their households. The brown tracts had connections reported for just 20% to 39.9% of households.
The new data, from December 2013, was posted on the FCC website in October.
Form 477 data includes the ratio of “residential fixed broadband connections” (i.e. home cable modem and DSL accounts) to total households — in other words, the percentage of households that had high-speed Internet service at the end of the reporting period — for each Census tract.
Starting with their last report, the FCC publishes separate data for household connections with speeds of at least 3 mbps down and 768 kbps up. Those are the connections I've mapped here.
Update: Now posted at Connect Your Community 2.0 site.