How to change the pattern background in legend keys?

I need to use colours and patterns independently to properly display my data, for this I use geom_col_pattern(). The issue I have is that in the legend the background is so dark, that the pattern is not clearly visible. It is not an issue of legend key size, as the pattern does show.

Here is the code I used:

library(dplyr)
library(ggplot2)
library(ggpattern)

mycars<-mtcars %>% head(10)
mycars$gear<-as.character(mycars$gear)
mycars$am<-as.character(mycars$am)

ggplot(mycars, aes(x=rownames(mycars),y=mpg, pattern=vs, group=gear, fill=gear))+
  geom_col_pattern(
    aes(
      pattern_density=am),
position=position_dodge2 (), 
pattern="stripe",
pattern_fill='grey40',
pattern_colour="grey40")+
  theme(strip.text = element_text(size = 4),legend.position="right", 
    axis.ticks.x = element_blank(),  axis.line.x = element_blank(),
    axis.text.x = element_blank(), axis.title.x=element_blank(),
  )

We could override the aesthetics of the legend keys to change the patterns spacing and fill color. I have also added colour = "black" to have a box around the keys.

ggplot(mycars, 
       aes(x=rownames(mycars), y=mpg, 
           pattern=vs, group=gear, fill=gear)) +
  geom_col_pattern(aes(pattern_density=am),
    position=position_dodge2(), 
    pattern="stripe", pattern_fill='grey40', pattern_colour="grey40") +
  theme_bw() +
  theme(strip.text = element_text(size = 4), 
        legend.position="right", 
        axis.ticks.x = element_blank(),  
        axis.line.x = element_blank(),
        axis.text.x = element_blank(), 
        axis.title.x=element_blank()) + 
  guides(pattern_density = guide_legend(override.aes = list(
    pattern_spacing = 0.03, fill = "white", colour = "black"))))

^{Created on 2025-07-02 with reprex v2.1.1}