The data for this graphic was gathered over 6 weeks in August and September of 2010. Numbers are based on guest lists as presented on Late Night Lineups. Determining race/ethnicity can be a rather dicey and imprecise activity, and it's also worth noting that the relationship between census and guest numbers is not a pure one – for example, some of the guests I counted as white are British white people who are visiting the United States.
Of course, a few guests were neither White, Hispanic, Black, nor Asian. These guests were left out, as their numbers were insignificant on the whole, but this explains why only white people show up in the Daily Show chart, yet the level is at 96% rather than 100%. The Daily Show only has 1 guest per show, so the data set for that program is very small. It may well have looked a bit more diverse in another 6-week period.
Some other noteworthy quirks: Chelsea Lately is the only show to have more Asian guests than the census numbers would suggest. However, it's mostly the same couple of Asians featured repeatedly, as Chelsea Lately lists their rotating panel of comedians as guests along with their one interviewee. Lopez Tonight features more Hispanic guests than any of the other shows, but not by a very wide margin. Their black guests are more impressively numerous. Lopez Tonight is also the only talk show to feature fewer white people than the census data expectation.
Almost across the board (Jimmy Kimmel Live is the only exception), white guests are more numerous in the first guest spot than overall. On Letterman, the jump is an astonishing 78% to 97%. With women, it's more mixed. On some shows, more women show up in the first guest spot, while on others, the reverse is true. Given the limited data set, there may not be much of a pattern to that.
The inequalities shown here can't just be blamed on the shows. For example, The Daily Show covers politics, and politics is a field full of old white men. Overall, the shows reflect our popular culture... but they also help shape it. Clearly, some shaping up is needed.