Hi, I'm pretty sure scale_colour_grey this does the trick. If you're using RStudio and it looks weird in the plots viewer, click the zoom button and look at it that way to check.

library(tidyverse)

data(immigration)

# specify formula
f1 <- ChosenImmigrant ~ Gender + Education + LanguageSkills + CountryOfOrigin + Job + JobExperience + JobPlans + ReasonForApplication + 
  PriorEntry

# create plot object 
p <- plot(mm(immigration, f1, id = ~CaseID), vline = 0.5)

# adjust visuals
p +
  scale_colour_grey() + 
  theme_bw()
  theme(legend.position = "right")

The last two lines aren't necessary, but I think it looks better with them. That is, p + scale_colour_grey() should be fine on its own. Equally you can do it without saving the plot object of course:

library(tidyverse)

data(immigration)

# specify formula
f1 <- ChosenImmigrant ~ Gender + Education + LanguageSkills + CountryOfOrigin + Job + JobExperience + JobPlans + ReasonForApplication + 
  PriorEntry

# calculate mms
mm_immigration <- mm(immigration, f1, id = ~CaseID)

# create plot object 
plot(mm_immigration, vline = 0.5) + 
  scale_colour_grey()

Exactly. It’s a ggplot2 object so you can just + whatever further modifications you want to it. You may need to use an aes() if you want to change shape, fill, etc. rather than colour.