How to buy eggs to avoid dark specks
The spots aren't anything to worry about. 

From Egg Safety Center


  Eggs with blood spots and meat spots are fine to eat. Most eggs with blood or meat spots are detected by electronic spotters and never reach the market, but it’s impossible to catch them all. Blood or meat spots are caused by the rupture of a blood vessel on the yolk surface when it’s being formed or by a similar accident in the wall of the oviduct in the hen’s reproductive tract. Blood spots and meat spots do not pose a risk to human health when prepared properly.


In the US, eggs farmed commercially are "candled" to ensure that blood spots larger than 1/8 inch aren't sold, but sometimes spots are missed.

In brown eggs, the spots can slip through the cracks more easily because the shells are more opaque, and heavier breeds (the breeds that produce brown eggs) produce more eggs with spots.


  Blood spots are also more likely to occur in eggs from birds of “heavier breeds,” says Craig Coufal, associate professor and extension specialist at Texas A&amp;M University Agriculture &amp; Life Sciences Department of Poultry Science. “All brown egg breeds are heavier than a White Leghorn layer,” he told Quartz in an email, referring to the most common egg-laying hen breed in the US.


From Quartz

The same source goes on to say that free-range and organically raised chickens produce more eggs with spots than typical factory farmed eggs.


  For cost reasons, some organic egg producers rely more on small grains like oats and barley, which are less expensive than corn. A diet made up of a lot of small grains, says Bruce, can cause blood spots. Plus, hens laying organic eggs can range outside, and are therefore exposed to changing temperatures, says O’Sullivan. That “could potentially elevate the incidence of blood spots in these production systems.”


So, buy white, non-organic eggs to avoid blood spots, but don't let spots keep you up at night. Free-range chickens may have more blood spots in their eggs, but for my own personal ethical reasons, I am loath to recommend against buying free-range.