sRGB with the DCM

 I was doing some good old fashioned "Digital Color Meter"ing (a Mac app) to pluck colors out of a screen mockup - I'd get the hex values, put them into an HTML document, and then they were visibly darker... and DCM confirmed, it was a different shade reading out than I was putting in.

Turns out, you really gotta get the right setting for the output display:

"sRGB" seemed to get the most accurate color readings... "In the world of web browsers, the sRGB color space is the standard."