Is your background a different color than white? Use a transparent background:
ggsave("myplot.tiff", dpi = 300, plot = myplot, bg = "transparent")
To save your images in a high quality format that can be scaled for printing in a magazine or on a poster
ggsave("myplot.tiff", dpi = 300, plot = myplot)Match your poster aesthetic with
scale_fill_manual(values = c("#__", "#__", etc)Check this also
Need more adjustments for your graph? Try a ggplot-extension!