That purplish spotting is just normal pigment. Common in this type of orchid. If it were black or brown it could mean rot or death of an old leaf etc. but this looks normal.
Many including Spicerianum and spotted/dark colored complex paphs as well as many vini colored maudiae will normally show this kind of pigmentation on that location. Natural. no more worries!
Rule of thumb is that the more color you see at the leaf base, the more color you will see in the flower. Doesn't always work, but it is a pretty good indicator.