Check the named palette colour vector you created with tax_palette()
tax_palette_plot(named_pal_vec, max_n = NA)
ggplot
library(ggplot2)
data(dietswap, package = "microbiome")
myPal <- tax_palette(dietswap, rank = "Genus", pal = "brewerPlus", n = 40)
myPal %>% tax_palette_plot() # just to check the palette