This post from Realto.com has some a really powerful painting hack. It's called How to Match a Paint Color Without a Sample.
Here's how they suggest we do the almost impossible task of finding the exact paint color even without a sample:
A digital snapshot from your cellphone can never quite capture the exact shade (and you don't want to end up buying an ugly color by mistake just because of the way the wall looks on your phone).
Instead, an ingenious way to find the true depth of a tone is to match the paint ...