This color is PANTONE 187. Sometimes “Red”, sometimes “University Red”, but in most cases I’ve seen it, “CORNELL RED”.
According to Page 9 of the Cornell Campaign Style Guide (the #1 item on Google for “cornell red hexadecimal”), the hexadecimal representation is #B31B1B.
The style guide then contradicts itself and says the RGB equivalent is R-196 G-18 B-48. Because hexadecimal colors are literally just that – hexadecimal conversions of RGB values – this color would be #C41230
The second result on Google for “cornell red hexadecimal” is the Johnson School’s Guide to Graphic Style. On page 7, it identifies Cornell Red by the Pantone Color, and then provides the RGB as R-224 G-58 B-62. In hexadecimal, this converts to #E03A3E.
The Johnson School Guide To Graphic Style then provides a web safe color equivalent. While it has been a number of years since we were constrained to 216 web safe colors, the guide helpfully suggests #CC0000.
A former colleague who was in a position to know a lot about these sorts of things said that the red typically used in Medical College design was/is #990000. (One would hope it was the same red as the main campus, but perhaps not.)
Finally, the Cornell Visual Identity Guide. The Identity Team recommends #B31B1B and also provides the appropriate RGB conversion of R-179 G-27 B-27.
The Identity Team wins, not only for actually getting the color right, but for being the only one of the three sources that was consistent within its own answer.
I find myself Googling for this hex value at least twice a year, so for my future self: the Cornell Red hexadecimal value is #B31B1B.
(Thanks to Mark Anbinder for hashing this out with me.)