A color is set per series, as discussed here: How to set labels for eached coloured bar in Plots.jl's bar()? - #6 by xiaodai
You could do:
julia> bar([[i] for i ∈ x], [[i] for i ∈ y],
color = permutedims(ifelse.(y .< 0, "#db5a44", "#447adb")),
label = "")
