Change sparkline coloring in shiny DT table

Question

Below is the code to develop sparkline in R. Wanted to check if we can change the color . I mean the negative values to be black and positive values to be red

library(shiny)
library(DT)
library(data.table)
library(sparkline)

## Create demo data sets
my_mtcars <- data.table(mtcars, keep.rownames = TRUE)
names(my_mtcars)[1] <- 'car_id'

set.seed(0)
data_for_sparklines <- data.table(car_id = rep(my_mtcars$car_id, 5),
                                  category = 1:5,
                                  value = c(runif(80),-runif(80)))

sparkline_html <- data_for_sparklines[, .(sparkbar = spk_chr(value, type = 'bar',barColor = "black")), by = 'car_id']
my_mtcars <- merge(my_mtcars, sparkline_html, by = 'car_id')

spk_add_deps(datatable(my_mtcars, escape = FALSE))