Rokkostuumhuren.nl maintains contact with the Vrije Universiteit and the University of Amsterdam. You possibly found this website by recommendation of Bureau Pedel.

Most universities will give you brochures and information regarding the formality. As you probably already know it is common for research assistants (promovendi) to appear in white-tie.

Two paranymphs, also in white-tie, will attend and assist during the ceremony. The paranymphs play a symbolic role, similar to one's best man at a wedding.

The color of the waistcoat should be black if the ceremony takes place at the Vrije Universiteit or the University of Leiden.