How to generate a custom color scale for plotly heatmap in R

I would like to get a custom color scale which looks like for plotly heatmap (plot_ly(z = data, colors = customcolors, type = "heatmap"))

palette <- colorRampPalette(c("darkblue", "blue", "lightblue1",
                          "green","yellow", "red", "darkred"))
plot(rep(1,50),col=palette(50), pch=19, cex=3, xlab = "", ylab ="", axes = F)

and where the blue end represents 1 and red end represents 10^6 and plotted data would have varying values on this interval.