I'm trying to plot a biplot by R package PCAtools, and I want to highlight some classes that might be interesting. However, the points are crowded near 0 and overlapped. How can I make the points in red show front to grey? Thanks.

Here is the code I used: p is the result of PCA

biplot(p, showLoadings = TRUE, lab = NULL,
       pointSize = 1,
         colby = 'genus', colkey = c("Others" = "grey50",
                                "Bacteroides" = "#225EA8",
                                "Phocaeicola" = "#41B6C4",
                                "Parabacteroides" = "#C7E9B4",
                                "Prevotella" = "#FDD49E",
                                "Porphyromonas" = "#D7301F"),
    colLegendTitle = 'Genus',legendPosition = 'top')

biplot