The effect is similar to what can be done with G'MIC's "Posterize" but not with regular "Posterize", which doesn't pick colors well - when you try to have as few colors as possible, it just picks FFFFFF white, FFFF00 yellow and so on.
The problem of SLIC is that it may create straight lines on the borders of clusters. The problem of smart posterization is that it's too global, so it may place two different regions in the same "color bucket", but it doesn't make sense for them to have the same color artistically.
