Currently from the Gantt chart for releases the option to "Color bars by assignee" only applies to features within each release while the release bars remain the same color.
We often have multiple releases in flight at the same time, assigned to different devs.
I was able to achieve a color per release by creating a Custom Roadmap but because the custom roadmap can't be edited the same way a Gantt chart does I'm forced to look at both so I can edit the Gantt and view the custom roadmap.
https://big.ideas.aha.io/ideas/APP-I-2030 (Shipped) sounds very similar, and its product value seems to be comparable to this idea to me.