It's not always good to set colour/fill to grey about gghighlight HOT 1 CLOSED

library(ggplot2)
geom_area()$geom$default_aes
#> Aesthetic mapping: 
#> * `colour`   -> NA
#> * `fill`     -> "grey20"
#> * `size`     -> 0.5
#> * `linetype` -> 1
#> * `alpha`    -> NA
geom_density()$geom$default_aes
#> $fill
#> [1] NA
#> 
#> $weight
#> [1] 1
#> 
#> $colour
#> [1] "black"
#> 
#> $alpha
#> [1] NA
#> 
#> $size
#> [1] 0.5
#> 
#> $linetype
#> [1] 1
geom_bar()$geom$default_aes
#> Aesthetic mapping: 
#> * `colour`   -> NA
#> * `fill`     -> "grey35"
#> * `size`     -> 0.5
#> * `linetype` -> 1
#> * `alpha`    -> NA