What means 'Niv.' in Personal Records and the colours of the Graphs?

Niv. and the colours in the Graphs are levels from the MSS of the Dutch Swimming Federation (KNZB). Every letter means a certain level on a scale from A+ to K. These levels are used for determining Qualification times for the Dutch Championships and for talent lists used by the NOC*NSF.

More information can be found on: http://www.knzb.nl/verenigingen/wedstrijdsport/zwemmen/topsport/talentontwikkeling/meerjaren_selectie_systeem/