Change colour of each marker depending on a 4th dimension

Question

The easiest and most natural thing is to add jitter to your plot.

Data setup:

using Random
Random.seed!(0)
N=2000
dat=DataFrame(x=rand(1:5,N),y=rand(1:5,N),z=rand(1:5,N))

Plotting:

scatter3d(dat.x+rand(N)./10 .- 0.2, 
          dat.y+rand(N)./10 .- 0.2, 
          dat.z+rand(N)./10 .- 0.2)

However, if you want to use the colors this still can be done:

dat2=combine(groupby(dat,[:x,:y,:z]),nrow)

Having processed the data now let’s make a colormap (you might want to adjust it differently):

using Colors
cols = range(colorant"red", stop=colorant"green", length=maximum(dat2.nrow))

Time to plot:

scatter3d(dat2.x, dat2.y, dat2.z, color=cols[dat2.nrow])