Southern Park Blue-Green fountain pen ink made by P.W. Akkerman pen store in The Hague.
Originally made to celebrate their 100th anniversary, this ink comes in a vintage-style bottle with a narrow neck with a marble stopper, to create a well at the top to aid in filling pens.
Named for the Zuiderpark Stadion, a football (soccer) stadium in The Hague. (Source: Wikipedia) Ackerman