Poultry Talk Ontario (pto.ca)

Over Christmas my flock has been moulting or otherwise taking a break from laying. My wife bought a dozen extra large Brown eggs to bake with. They were a nice dark brown , but not as dark as a Marans My Orpington and some Sussex eggs are bigger. Also 5 out of the 12 eggs had blood spots! Go figure.

Blood spots in brown eggs are more predominate than white because seeing the spot at candling is harder sometimes near impossible with brown shells. Small blood spots aren’t an issue but some folks don’t like to look at um so just pick out with something.
Survey says, store bought caged layer white eggs are about 1% with spots & brown 5% . Also depends on how hens are raised .

Production hens at their peak will naturally have more blood spots because their egg follicles are highly vascularized. Production hens in layer barns also get/carry Infectious Bronchitis, which can affect the reproductive tract and cause petechial bleeding--their small blood vessels are more 'leaky' than those of healthy hens. As Ross said, you will find lots of them in brown eggs because they're harder to see at the candling station, and only the big ones are (usually) caught. Even if they're seen, they're allowed to pass the egg if the spot not greater than 1/8 inch.