The Matrix graph can have a plain background, or a background image. If you have a heat map image that you like, save that to your computer and upload it to your Matrix process. An alternative is an overlay (colour coded grid/cells background)
To change the background of your heatmap:
Click on Graph Settings
Click on Matrix Graph. Then if you wish to use a background image file, click on background. If you want to set up a colour coded grid type background click on Overlays.
OR
If uploading a background, browse to the image file that you wish to upload and then click OK. If you want the background image to show automatically when the heat map is displayed, tick the Auto show box prior to clicking OK.
If using an Overlay, right click on each cell to change the format. The Background option will allow you to change the colour and style of the cell.
Note that styles can be copied from other cells and pasted.
If the cell doesn't not display the chosen colour, check that there is a tick (cheque mark) next to the word Visible in the right click menu.
If you want the overlay to show automatically when the heat map is displayed, tick the Auto show box prior to clicking OK. If you have previously used a background image (or an image is set on the template you have used), ensure that the Auto show on the background settings page is not ticked.
When you are displaying your results on the heat map, the Show/hide button allows you to choose between overlay, boundary, background image or no background,