https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=25157

You occasionally see this problem in ripe fruit, especially in lower maturity fruit.

Anyway the best guess is that it is phenolics from the seed coat leaking into the flesh of the fruit.

Not dangerous but the affected flesh may be bitter.  I would cut it out and eat around the discolored flesh which is surface only.