Per-cell Border Colors In A Highcharts Heat Map

I'm using highcharts to create a simple heatmap, but now I want to use custom border colors on the cells to represent another dimension in my data set. I am able to accomplish this

Solution 1:

It is possible to add pixel padding for a heatmap series and set borderWidth to double of set padding.

Example: http://jsfiddle.net/jk9hp3y9/2/

Example based on your demo: http://jsfiddle.net/8ft7e923/2/

As Halvor mentioned - it is not yet possible to set border for SVG elements to be placed inside of element.

Another way could be to extend Highcharts (similar as in provided demos) to change size of cells with border set to make them fit in same place as the ones without border. More about extending Highcharts in Docs.