It is possible that this is evidence of a previous fungal infection. Drying the wood can trigger the colorations. Specific fungi can change woods so specific colours can later appear. I don't see the rest of the board in the picture but would you say that the discoloration follows the grain?
I found a pdf called Discolouration of timber in connection with drying. A section described a yellow stain that follows the grain which was caused by
Metabolization of tannic acids by the fungus:
In trying to find another resource I found a Google book Wood and Tree Fungi: Biology, Damage, Protection, and Use which stated:
Paecilomyces variotii produces a yellow discoloration of oak wood during drying times through its pH-change, which causes chemical reactions of the hydrolyzable gallotannins.
While that quote states "oak wood" this fungus has been found on many wood species so it is not a stretch to think that is what you have here.
What does this mean?
Assuming I am right there is nothing wrong with the wood. This colour should not penetrate too far and you should be able to plane it off.
This is related to the process of spalting where molds and fungi are used to naturally colour wood.
I don't think there is a safety risk here if the above proves to be true. Not sure what else could have caused that colour.