Obsolete warning when plotting contour lines in GR ?

[fhagemann]

When I use contourf with the backend gr(), it looks like I can choose the color of the contour lines arbitrarily.

using Plots; gr()
x = -10:0.1:10
y = -10:0.1:10
data = x.^2 .+ y'.^2
contourf(x, y, data', ratio = 1, seriescolor = :viridis, linecolor = :black, size = (510,500))

However, when I choose anything other than linecolor = :black, the contour lines appear in the color I want, but I get a warning that only black contour lines are supported.

using Plots; gr()
x = -10:0.1:10
y = -10:0.1:10
data = x.^2 .+ y'.^2
plot(
    [contourf(x, y, data', ratio = 1, seriescolor = :viridis, linecolor = c, size = (510,500)) for c in [:white, :red, :green, :blue]]...,
    size = (2000,2000)
)

 Warning: GR: filled contour only supported with black contour lines
└ @ Plots /user/.julia/packages/Plots/nbICw/src/backends/gr.jl:2036
 Warning: GR: filled contour only supported with black contour lines
└ @ Plots /user/.julia/packages/Plots/nbICw/src/backends/gr.jl:2036
 Warning: GR: filled contour only supported with black contour lines
└ @ Plots /user/.julia/packages/Plots/nbICw/src/backends/gr.jl:2036
 Warning: GR: filled contour only supported with black contour lines
└ @ Plots /user/.julia/packages/Plots/nbICw/src/backends/gr.jl:2036

Is this warning still needed?
Because it looks to me like filled contour is supported with any color contour lines..

Versions

Plots version: 1.34.3
Backend: GR 0.69.1
versioninfo():

Julia Version 1.8.0-rc1
Commit 6368fdc656 (2022-05-27 18:33 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: 128 × AMD EPYC 7702P 64-Core Processor
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-13.0.1 (ORCJIT, znver2)
  Threads: 32 on 128 virtual cores

[t-bltg]

I guess it's reasonable to remove this warning.