Talent: If you have played another minion here this turn, draw a card.
This is a reasonable interpretation, limiting the time per turn to match the talent usage. This solves long-term memory issues (remembering what's been played, moved and removed) and also has the game effect of encouraging the player to continue playing minions in the same place, which suits the faction well.
This is also supported by Barliman on BGG, who says that this was the intended functionality during playtesting.
Under this interpretation (and the RAW interpretation coming next), it doesn't matter if the qualifying minions were played and subsequently removed. It also won't work if minions have only been moved there.
Read as written:
As a talent, you can draw a card if you have ever played a minion other than that Rainbow on the base that Rainbow's currently on. This functions similarly to the above rule mechanically, but without the time limit and without a reason for the player to continue piling minions up.
Talent: If you have another minion here, draw a card.
While this seems like a reasonable way to play the card, it would be odd that it wasn't worded like this. It's not too dissimilar, but it doesn't remotely match the way the card is written.