When I make a mosaic plot with default shading shade=T the p-value displays under the legend
mosaic(~ gear + carb, data = mtcars, shade=T)
When I instead use Friendly2 shading, I don't get the p-value.
mosaic(~ gear + carb, data = mtcars, gp=shading_Friendly2)
I think the best approach to this would be to use a different shader that contains the p-value by default (like shading_hcl) and then modify the color of that shader ( https://rdrr.io/cran/vcd/src/R/shadings.R )
So to make your example working with that new shader:
cars <- table(mtcars$gear, mtcars$carb)
mosaic(cars, gp = shading_hcl(observed=cars, eps=0.01, lty=1:2, h=c(260,0), c=c(200, 200), l=c(90, 50)))
