Off topic:How to make the boxplot outline black and only keep dots colorful?

Question

[Raheleh]

Hello folks,

I made this boxplot:

This is the script:

p_C <- ggplot(data, aes(x = group, y = Cytotoxic.lymphocytes, color =factor(group)))+geom_boxplot()+geom_quasirandom(width=.1)+labs(y = "CTL /MCP")+theme_bw()+theme(legend.position = "none", plot.title = element_text(hjust = 0.5),axis.title.x=element_blank(), axis.title.y = element_text(size = 13, face = "bold", family = "Tahoma"),axis.text.x = element_text(size = 13, face = "bold", family = "Tahoma"), panel.grid.major =element_blank(), panel.grid.minor = element_blank(),panel.background = element_blank(), panel.border = element_blank(), axis.line = element_line())

#### Add p-value
p_C+geom_signif(comparisons = list(c("Relapse", "nonRelapse")), 
                map_signif_level=TRUE, color = "black")

I want to make my boxplot outline black and only keep the dots colorful to show the groups. Can anyone help me? I tried to do it by scale_fill_manual()but nothing changed.

Many thanks!