Emulating plotly's contour map color distribution

[Larry Martell]

I am using a javascript ploting package called plotly and I use that
to generate a contour map. In that package you define a rangeMin,
rangeMax, and binSize, and you give it a color map, e.g.:

[["0", "rgb(0,0,0)"], ["0.3", "rgb(230,0,0)"], ["0.6",
"rgb(255,210,0)"], ["1", "rgb(255,255,255)"]]

This specifies the color you want at the endpoints of the range, and
at the 1/3 and 2/3 points. Given the range and binSize plotly
calculates the number of bins and distributes the color uniformly
across the range, coloring the contour map appropriately given the
data.

I have another legacy map not generated with plotly and I want the
colors of that to match the plotly map. In the legacy map I have the
rangeMin and rangeMax and the binSize (although the binSize is not
currently used). It currently determines the color for each value like
this, in python:

COLORS = ('#ff9', '#ff0', '#fc0', '#f90', '#f60', '#f00', '#930', '#800000')
normal = (value - rangeMin) / (value_max - rangeMax)
ordinal = int(normal * len(COLORS))
if ordinal == len(self.COLORS):
    ordinal -= 1
color = COLORS[ordinal]

I am looking for some advice on how I can modify this to generate the
same colors as plotly would, given the same data set and range and bin
size.