@jezlax The normalization of range ends, above, was necessary to define the discrete colorscale. The original values are also normalized by plotly.js in order to map them to the coresponding color.
You only have to insert a suitable text as a colorbar ticktext (see the image below).
I detailed all ingredients needed to plot a heatmap with a discrete colorscale in this notebook https://plot.ly/~empet/15229.
