I did some research for a potential niche side collection today and want to share my findings. These are all the cards with rainbows in the background. I prefer the earlier ones - the later ones feel more generic and uninspired.
Feel free to let me know if I missed anything!
I remember someone on Reddit sharing a rainbow collection before, and the one that stood out to me was good ol Jungle Bellsprout (I was like “really?!” And had to look up an image of the card). It’s faint, but it’s there!
You’re missing at least two off the top of my head:
Togetic definitely qualifies – Togepi is arguable because it’s just a reflection of a rainbow.
insert all rainbow energies
This card is part of my Eeveelutions collection and I look at it often…hadn’t ever noticed it had a rainbow 
Rainbows really are everywhere if you pay attention!
First card that came to mind:
Pairs of cards that complete a background with a single rainbow is the subcollection within a niche collection that I didn’t know I needed.
