About 25-30% of brown eggs, irrespective of brand, typically have what are referred to as pigment or protein spots next to the yolk or floating in the albumen. If you look very closely at white eggs, you will see that they have similar particles of protein floating around, but the hens lack the brown pigment in their system that combines with the protein to make them stand out. The spots are not an indication of fertility and they do not contain any blood cells, as would a true blood spot. The spots can be removed with the tip of a knife, if preferred, but they are also perfectly safe to leave. The red-colored blood spots are also safe, but most people prefer to discard bloodspot eggs. It is difficult to detect interior defects when shining a candling light through a brown-shelled egg, so bloodspots are also more frequently found by consumers in brown eggs than whites. There is probably a 1 in 3000 chance of finding a blood spot in a white egg and 1 in 1000 chance in a brown egg.
The American Egg Board Eggcyclopedia provides the following information regarding blood spots:
"Blood spots: Occasionally found on an egg yolk. These tiny spots do not indicate a fertilized egg. Instead, they are caused by the rupture of a blood vessel on the yolk surface during formation of the egg or by a similar accident in the wall of the oviduct. Mass candling methods reveal most eggs with blood and those eggs are removed. However, even with mass scanners, it's impossible to catch them all. Both chemically and nutritionally, eggs with blood spots are fit to eat. You can remove the spot with the tip of a knife, if you wish."