What a sight! It looks like a major update on Workshop, where a tool (previously void) shifts a particle's color to a new one (that is, changing the color).
Be noted that the changes only applies to ultimates' particles. So yeah, basic abilities are still in their actual color.
Nonetheless, I tried it myself, only to change the particles to full green (0,255,0), and Voila! It may be different from actual in-game later (primarily based on the color shift), but here you go. It's official.
Freezing Field (falling shard):
Finger of Death: