Yes! Markings on wood are completely normal, and 99.99% of the time, they do not result in a fault.
These markings can vary from a very subtle grain, to dark mineral marks and knots.
Most toy manufacturers embrace these unique markings, and will only discard a piece of material if it will cause problems during manufacturing and/or play. This is to reduce waste, and also because these unique markings are seen as a beautiful, natural addition to the toy.
But what can you expect from wood? Here are some descriptions of the markings you may encounter:
Wood Grain: This refers to the lines that naturally run through wood. Their formation changes as the tree grows, and how they appear during manufacturing depends on the direction the wood is originally cut. The color ranges from very light, to very dark.
Mineral Marks: These darker marks are created during growth after the tree has absorbed different minerals from the soil and has deposited them in its wood. They vary in colour, from light to dark, and the size and shape varies from anything between small and round, to large and long.
Wood Knots: These are a very common characteristic in wood. They are present at the point where a branch has grown, and can run deep into the trunk. The sizes vary from very small, to quite large. The texture varies too, sometimes they can be completely smooth, but sometimes they can be cracked, which is completely normal.
Fluffy Texture: Sometimes, you may find that part of your wood has some texture, what can be referred to as fluffy or fuzzy. Although it isn't common, it isn't harmful and is something that can be expected during manufacturing. This can be a product of a piece/area of wood with low density or high moisture, and the direction of the grain in the manufacturing process can contribute to the finish. You may find that it is a little rough, but it wouldn't splinter or cause harm so more often than not, you would find a manufacturer won't treat this as a faulty piece of wood.
Spalting: This is a colour variation in the wood caused by fungi that grows in trees and feeds on their nutrients. This results in patterns being left behind, often as dark dots and lines, but you can also find a patchwork or marble effect too. This is completely harmless and perfectly safe, as any harmful wood would not be used for toys.