A quantitative analysis of the graying of Barack Obama's hair
pnis.co
pnis.co
I love this kind of 'research'. It's frivolous, but there is an underlying point about the stressfulness of presidency.
Source: http://pnis.co/about.html
If a politician is too old - dye out some (or all) of the gray. Reagan being an extreme example - not a single gray hair.
If a politician is young - Clinton, Bush, Obama - add some gray, until nature catches up.
Gray hair conveys "gravitas" - age, and experience - exploits a natural human bias. I'm sure this is focus-grouped to death. This all being in the age of Color TV and HDTV of course - I doubt Kennedy stooped to this level. Pretty punishing, and just imagine a 4K picture or better down the road.