colorbar(p, ..., limits = NULL, which = 1)

p <- plot_ly(mtcars, x = ~wt, y = ~mpg, color = ~cyl)

# pass any colorbar attribute -- 
# https://plotly.com/r/reference/#scatter-marker-colorbar
colorbar(p, len = 0.5)

# Expand the limits of the colorbar
colorbar(p, limits = c(0, 20))
# values outside the colorbar limits are considered "missing"
colorbar(p, limits = c(5, 6))

# also works on colorbars generated via a z value
corr <- cor(diamonds[vapply(diamonds, is.numeric, logical(1))])
plot_ly(x = rownames(corr), y = colnames(corr), z = corr) %>%
 add_heatmap() %>%
 colorbar(limits = c(-1, 1))