mapbox error: unknown function colorize-alpha(), did you mean sobel(0) (line 73)

Question

I installed mapbox on ubuntu locally and I am trying to create a heatmap following this article: https://www.mapbox.com/blog/colorize-alpha-image-filter/. I uploaded some point data and tried to style the layer using this style sheet:

{
    image-filters:colorize-alpha(teal,green,yellow,orange,red);
    comp-op:multiply;
    marker-allow-overlap:true;
    marker-file:url(/images/marker.png);
} 

When I save the project I get this error: mapbox error: unknown function colorize-alpha(), did you mean sobel(0) (line 73)

Here is the tilemill version info:

dpkg -s tilemill
Package: tilemill
Status: install ok installed
Priority: extra
Section: web
Installed-Size: 164411
Maintainer: Ian Ward <ian@developmentseed.org>
Architecture: amd64
Version: 0.10.1~precise2
Depends: libc6 (>= 2.14), libgcc1 (>= 1:4.1.1), libglib2.0-0 (>= 2.12.0), libgtk2.0-0 (>= 2.8.0), libmapnik (>= 2.1.0), libstdc++6 (>= 4.6), libwebkitgtk-1.0-0 (>= 1.3.10), zlib1g (>= 1:1.1.4), debconf (>= 0.5) | debconf-2.0, nodejs (>= 0.8.10), libsqlite3-0 (>= 3.6), libsqlite3-dev
Suggests: postgis
Conffiles:
 /etc/logrotate.d/tilemill.rotate 561d43af38d7890cab74ff103e8ba0c9
 /etc/init/tilemill.conf 3654de7aeee4893a705df3ed4ec00174
 /etc/tilemill/tilemill.config f2b0b4555cbeaed2506565b32941f435
Description: A modern map design studio.
 A modern map design studio powered by open source technology.
Homepage: http://github.com/mapbox/tilemill

Answer 1

The colorize-alpha feature is not available in TileMill 0.10.1. To use it you'll need a development version of TileMill, eg by building from source.