This blogpost shows in a few steps how to add a continuous colour legend for a raster layer in a map layout in QGIS. It is a work around, but it works.
Programs like R and GRASS GIS are incredible powerfull. But occasionally you'll need a functionality that is not available yet. Luckily, depending on the kind of functionality, it isn't terribly difficult to create your own scripts. In the past years I have created a few scripts that I hope are useful to others as well.
Throughout the years I have used a wide range of open source GIS, database and statistical software both for personal and professional use. In order not to forget newly learned techniques or tricks I try to jot down some notes whenever I have learned something new. And occassionally, I write them down on my blog, in the hope that they come in handy one day for somebody else.
Website of the OSGeo.nl foundation.