Optricks

"The coloring for these objects needs to have 

the randomness of reality,

but also include as much variation as possible within a believable visual range. 

It’s an imprecise

 mixture 

that’s tricky to achieve."

FULL ARTICKS:

http://www.fastcocreate.com/3021426/see-history-in-a-whole-new-light-with-classic-black-and-white-photos-now-in-living-color#9