One is for collection and one is for RG!
in theory everyone is a rainbow here
Just start by blooming 16 gold or better of each color. Event girls are fine. Then start running whale to get the free tickets and the good equipment.
Recommend saving stones to RG Rainbow Rose as she will come around again to acquire and it will help greatly to have the mats ready
When the rare Tokubetsu Mission comes around, stock up on mats for a year!
Edit : and buy the 90 FS rainbow Kugaisou. She is good.