On episode 18 of the Loopcast, Sina and his guest discuss fashion and national security. Around 23:00 comes the money quote: "There's a lot of black hair dye involved being a dictator." Here's the logic:

[I]n a democracy, your hair turns grey very quickly in a four year term.... But in a dictatorship, the hair gets oddly darker: it just turns to an eerie shade of black.... [Dictators] want to remain relevant. They didn't want to get old.... They didn't want it to seem like they had been getting old and getting crushed by the responsibility of their job.

While a random sample of hair shades and a thorough hypothesis test is beyond the scope of this post, I'll let the readers judge for themselves based on the photos below. Note that one source of bias may be that US presidents try to look young and vital for the election but let their hair go after that.

Democratic Leaders:

[caption id="attachment_2342" align="aligncenter" width="590"]Bill Clinton, 1993 and 1999 Bill Clinton, 1993 and 1999[/caption]

[caption id="attachment_2343" align="alignright" width="590"]george-w-bush-2001-2008 George W. Bush, 2001 and 2008[/caption]

[caption id="attachment_2344" align="alignright" width="590"]barack-obama-2009-2011 Barack Obama, 2009 and 2011[/caption]

(More US president before/after photos here.)

Dictators:

[caption id="attachment_2345" align="aligncenter" width="313"]Hosni Mubarak in 2012: Imprisoned and hospitalized but not grey Hosni Mubarak in 2012: Imprisoned and hospitalized but not grey[/caption]

[caption id="attachment_2346" align="aligncenter" width="594"]Muammar Qaddafi ruled Libya for 42 years Muammar Qaddafi ruled Libya for 42 years[/caption]

[caption id="attachment_2347" align="aligncenter" width="640"]Hugo Chavez not letting grey get the best of him Hugo Chavez kept grey at bay until the very end[/caption]