I did find that too unfortunately it seems (or I missed something) that you can’t change alpha/trasparency in the gradient of the color of explosion particles though (=no transparency at all)
edit: nvm, you have to click the downward arrows on the top of the color picker to choose transparency
In 2019.4.13f1 (LTS) I decided against using the legacy and went with the standard unlit shader. You just have to change the rendering mode to one of the options that shows the sprites the way you like. I used “Cutout”
I noticed when I was playing with the particles that having the alpha below 127 caused most to not render. Maybe it was this Alpha Cutoff setting… I’ll play with that and see what difference it makes.