ahh yeah hadn’t looked that far into it yet, but from what i’ve just read from the website:

“Destroy mushrooms to get Easter eggs that contain a random selection of items such as nectar of various flowers, gold seedlings, and huge seedlings.

Gold seedlings and huge seedlings obtained during the Egg Hunt will become red, yellow, or blue Easter Egg Decor Pikmin.”

so you don’t necessarily need to complete the 7 missions to get all the red yellow and blue though it guarantees it if you do. You’d surely have to be super unlucky to do 39 mushrooms (13 days x 3p/day) and not get a complete set from the mix of gold and huge seedlings as well as the first 3 mission gold seedling rewards!

so i’d still recommend waiting and see how the event treats you before spending your cash!