# Colours from a \[0,1\] float?
**URL:** https://discourse.julialang.org/t/colours-from-a-0-1-float/112866
**Category:** Visualization
**Tags:** colors
**Created:** [April 12, 2024, 9:28am UTC](https://discourse.julialang.org/t/colours-from-a-0-1-float/112866 "2024-04-12T09:28:50Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)
#### Post date: [April 12, 2024, 9:28am UTC](https://discourse.julialang.org/t/colours-from-a-0-1-float/112866/1 "2024-04-12T09:28:50Z")
I have some data that I want to represent in a histogram with a different colour of the bin that depends on a float in the 0,1 range.
I can see I can pass to the histogram call a `colour` parameter with the vector of colours, but how do I create the colours when my “colour data” is in the range [0,1] ? For example, 0 is a full green colour, 1 is a full red one, and I want a colour associated to 0.2 (so, mostly green).
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### Author:  [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)
#### Post date: [April 12, 2024, 9:35am UTC](https://discourse.julialang.org/t/colours-from-a-0-1-float/112866/2 "2024-04-12T09:35:15Z")
Got it:
`weighted_color_mean(0.2, colorant"red", colorant"green")`
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### Author:  [@ffevotte](https://discourse.julialang.org/u/ffevotte)
#### Post date: [April 12, 2024, 10:05am UTC](https://discourse.julialang.org/t/colours-from-a-0-1-float/112866/3 "2024-04-12T10:05:29Z")
You might also want to use [`ColorSchemes.jl`](https://github.com/JuliaGraphics/ColorSchemes.jl): after all a color scheme is nothing but a tool that maps a scalar value into a color.
I don’t know about your specific use case, but using a fully-fledged color may have several advantages w.r.t a simpler, more manual technique like you did:
1. the relationship between colors may be more complex than a simple mean ;
2. I’m no expert myself, but I know that a lot of research has been spent devising color schemes that are “good” (considering what the human eye perceives, and how visually impaired persons might be affected) or simply visually appealing ;
3. you benefit from a very large [catalogue](https://juliagraphics.github.io/ColorSchemes.jl/stable/catalogue/) of schemes to choose from.
For example:
```julia-repl
julia> using ColorSchemes
# this comes from the `colorcet` collection and has green on one end,
# white in the middle and red on the other end. But you may choose any
# other color scheme and still get a consistent API for accessing the
# colors in it.
julia> cs = ColorSchemes.diverging_gwr_55_95_c38_n256;
julia> get(cs, 0.1)
RGB{Float64}(0.39467,0.662455,0.270175)
julia> get(cs, 0.9)
RGB{Float64}(0.958145,0.43425,0.391305)
```
---
### Author:  [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)
#### Post date: [April 12, 2024, 10:18am UTC](https://discourse.julialang.org/t/colours-from-a-0-1-float/112866/4 "2024-04-12T10:18:02Z")
> [@ffevotte](#):
>
> ```julia
> cs = ColorSchemes.diverging_gwr_55_95_c38_n256;
>
> julia> get(cs, 0.1)
> RGB{Float64}(0.39467,0.662455,0.270175)
>
> julia> get(cs, 0.9)
>
> ```
Thanks. Can the “limits” of the colour scheme be specified programmatically?
This is the function I am ending up using, where I specific the lower and upper bound colours:
```julia
function generate_bin_colours(data,classes,bins;lcolour=colorant"green",ucolour=colorant"red")
# Creation of shares per bin
nbins = length(bins)
ndata = length(data)
shares = zeros(nbins-1)
for ib in 1:nbins-1
ndata_per_bean = 0
sum_per_bean = 0.0
bin_l = bins[ib]
bin_u = bins[ib+1]
for id in 1:ndata
if data[id] >= bin_l && data[id] < bin_u
sum_per_bean += classes[id]
ndata_per_bean += 1
end
end
shares[ib] = ndata_per_bean > 0 ? sum_per_bean / ndata_per_bean : 0.5
end
return [weighted_color_mean(x, lcolour, ucolour) for x in shares]
end
```
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [April 12, 2024, 11:10am UTC](https://discourse.julialang.org/t/colours-from-a-0-1-float/112866/5 "2024-04-12T11:10:00Z")
> [@sylvaticus](#):
>
> Thanks. Can the “limits” of the colour scheme be specified programmatically?
Yes. See: [Color Range: pick color in range base on values in a vector - #4 by stevengj](https://discourse.julialang.org/t/color-range-pick-color-in-range-base-on-values-in-a-vector/80533/4)
> [@sylvaticus](#):
>
> `weighted_color_mean(x, lcolour, ucolour)`
As explained in the linked post, doing linear interpolation like this produces a color map that is not perceptually uniform (distorts data).