I have run into a persistent bug when using the Particle Designer UI on Mac Sierra.
The color picker in the PD user interface intermittently selects and initializes the chosen color, (Start Color and End Color picking)
I found a similar issue from 2014 here
https://forums.coronalabs.com/topic/49088-particle-designer-color-issue/
Through shear determination and fiddling (resetting the blend source, blend destination, variance and emitter ) I can sometimes select/iniitalize a color however cannot find the pattern/trigger as yet.
The PD manufacturer website seems to be pretty ghost town but will post here also if no ones has any ideas or workarounds/hacks. I have updated PD to latest version also. (2.9)
Mac OS Sierra - 10.12.6
Particle Designer - 2.9