Guardian’s Song: And, if you continue on with the analogy, Jessie’s hair looks purple in some shots, and the inverse of purple is yellow… So she’s endorsing Jessie/Cassidy as well.

I always thought Cassidy had Orange hair (checks image on Bulbapedia).
Eh. Still looks Orange to me. I can see where you are coming from though.
Honestly, Jessie/Cassidy would be a more functional pairing than Jessie/James in this fic