I am not sure if this helps you, but when I pass the whole tab10 palette to plots, an incorrect colorscheme shows up in the plot. But when I pass a truncated palette that matches the number of groups in the plot, I get back the correct colors, i.e., the difference in the palette keyword below:
using Plots, ColorSchemes
gr()
fullpalette = plot(1:100, rand(100), group=repeat([1,2,3,4,5], inner=20), lw=3, palette=ColorSchemes.tab10.colors, title="Full palette");
truncatedpalette = plot(1:100, rand(100), group=repeat([1,2,3,4,5], inner=20), lw=3, palette=ColorSchemes.tab10.colors[1:5], title="Truncated palette");
combinedplot = plot(fullpalette, truncatedpalette, size=(1600,800))
savefig(combinedplot, "tab10_colorschemes.png");
Which produces the following:
