Hi there!
Shield Rush has the physical tag, and its explosion is red. With the Dark Rush node, it gets a Void tag, and its explosion is void-y purple instead.
With the Echoes of the Charge node, you can have a second explosion added after the first. However, with both Dark Rush and Echoes of the Charge allocated, while the first strike is correctly purple, the second one is still red, as if the void “conversion” wasn’t happening.
Link to a video here.
Thanks a lot for your work! 