Hi,
I uploaded a version of the colour-gradient as Blockly Plugin on Github. You can clone it from Github
https://github.com/SPE-Systemhaus/blockly-colour-gradient or install it with bower by typing:
bower install --save blockly-colour-gradient
I'm sorry for waiting so long to get a response, but I was a little busy ... I wrote my master thesis and following this there were some other projects todo before I had time to update/rework the colour-gradient ;-) It works with the current Blockly version on Github.
Cheers,
Michael Kolodziejczyk