library(ggplot2)
# To reproduce this error shadowtext is installed from source, not binary.
library(shadowtext)
set.seed(1)
d <- data.frame(x = rnorm(3), y=rnorm(3), label = c('hello', 'world', '!!!'))
ggplot(d, aes(x,y)) +
geom_shadowtext(aes(label=label, color=label), bgcolor='firebrick')
#> Error in col[, rep(1, length(alpha)), drop = FALSE]: subscript out of boundsCreated on 2018-09-27 by the reprex package (v0.2.1)

bg.colorhere is renamed tobg.colour:https://github.com/GuangchuangYu/shadowtext/blob/dc47ac7f991745eb7918c136d7260c27d878bf75/R/geom-shadowtext.R#L73