Create a discrete color scale to be used for the plot.
Scale.discrete_color is an alias for Scale.color_discrete_hue.
levels(optional): Explicitly set levels used by the scale. Order is respected.
order(optional): A vector of integers giving a permutation of the levels default order.
This forces the use of a discrete scale on data that would otherwise receive a continuous scale:
plot(x=rand(12), y=rand(12), color=repeat([1,2,3], outer=), Scale.color_discrete())