I get the same as you with no space after the colon (get warned) and with space after the color (no warnings).
I tried a bunch of other sites without the space and not one delivered the warning. I suspect site design problems at FR rather than something nefarious. It might be the 1995 web design.
washingtonpost.com
slate.com
democratunderground.com
salon.com
rushlimbaugh.com
time.com
nationalinquirer.com
dailycos.com
ijreview.com
infowars.com
breitbart.com
Same here as well, it is the redirect pages that are causing the issue, but the returns on a site search with a space between the “site:” modifier and URL return much less information and within a few hits the results point to other sites, not FR.