List of expensive balls of yarn -

If you get a minipet this color @ Fasoro Falls it may be beneficial to sell it. Best ones are bolded

Breeze (400k)
Bronze (450k)
Chocolate (500k)
Digital (200 Dukka, none on search)
Eleka (500k)
Fade (1.1M, retired)
Gem (3.8M, beanstalk)
Ghost (450k)
Gold (400k)
Halloween (10M, retired)
Lilac (1.1M, old fairy)
Moonlight (2M, moonlight fairy)
Negative (2.5M, farmer)
Nimbus (1.1M, nimbus goals)
Plant (425k)
Seasonal (4M, retired)
Rainbow (900k, lush lake)
Radioactive (500k)
Space
Splatter
Spring
Summer
Toy
Winter