I think you can use the continuous_color_gradient scale 
<http://gadflyjl.org/scale_continuous_color_gradient.html> element. So 
maybe something like:

spy(rand(5,5),Scale.continuous_color(minvalue = 0.1, maxvalue = 0.9))

Values that are outside the specified range will be black.  You can also 
get more direct control over the colors by using the ContinousColorScale 
<http://gadflyjl.org/scale_ContinuousColorScale.html>.  

On Wednesday, November 19, 2014 12:36:23 AM UTC-8, JVaz wrote:
>
> Does anyone know how to fix the colors of the legend, independently of the 
> values to plot? For example, even if all the values of the matrix to plot 
> are 0, I still want the legend to go from -1 to 1, to keep all the 
> different plots uniform.
>
> I've been reading a lot here, but didn't find it:
> http://dcjones.github.io/Gadfly.jl/geom_rectbin.html
>
> El viernes, 14 de febrero de 2014 09:38:16 UTC+9, Elliot Saba escribió:
>>
>> Hey there, I'm trying to use Gadfly's Geom.binrect to plot a matrix, but 
>> I can't figure out how to do it without going through a lot of rigamarole 
>> to generate a DataFrame like is used in the example 
>> <https://github.com/dcjones/Gadfly.jl/blob/master/doc/geom_rectbin.md>
>>  docs.
>>
>> I have, say, a 10x10 matrix:
>>
>> z = randn(10,10)
>>
>> In matlab, if I wanted to plot it, I would just imagesc(z).  I know that 
>> if I had a dataframe with a row for each point in z stored in a column, and 
>> the x/y coordinates recorded in their own columns, I could coerce Gadfly to 
>> plot what I want as shown in the example.  But is there a simpler way to do 
>> this?  I've tried something like:
>>
>> plot(x=1:10, y=1:10, color=z, Geom.rectbin)
>>
>> But Gadfly just plots one pixel for each x and y passed in.  I understand 
>> why it's doing that, I just don't know the easiest way to get it to treat z 
>> as a matrix, instead of a vector.
>>
>> Thanks,
>> -E
>>
>

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