Automatic: the lightest end just below the closest wins (never below 50 % in a run-off); the darkest where each party's top 10 % of wins begin, averaged over the parties by the areas they win, so only the biggest strongholds are darkest and one party (e.g. Aliancia) doesn't wash out the rest.
Data: Štatistický úrad SR · ZBGIS © ÚGKK SR (CC-BY 4.0) · Register adries MV SR · © OpenStreetMap contributors (ODbL) · Kiesraad · CBS / PDOK