You are right, Christoph.
Black background brings up the best colours, due to the contrast between no colour and colours.
White background is probably the worst becasue white is tt bright and kills the colours, which become too dark! the white therefore become too shiny to the eyes.
But other backgrounds lighter can be useful if associated as complementar to the dominant colour of the painting. The tone is softer, Grey is neutral, more 'universal', but others would also fit.
Here are some examples or a red painted subject.