In 1959, they did do bit of a larger study, but measured color across 10 degrees instead of the 2 degrees in the original study, so the data isn't quite directly comparable. It had a sample size of 49 people, though four of those people did the test twice.

Source:
www.cvrl.org/stilesburch1...

Not as different as you might think. Here's a plot of the variation measured in 10 different people in 1955.

Source (has this figure, an excel spreadsheet of the data, and more in-depth descriptions of what it means (by clicking the circled i by 'Further information')):
www.cvrl.org/stilesburch2...