This one is from tom, who was also involved in the original video. This design is all clear skies and rainbows! 
— Website description[1]
reverse rainbow (逆さまレインボー Sakasama Reinbō?) is an Outfit for Kagamine Len.
Description[]
The Outfit's attire consists of a long white coat with yellow inner-fabric, a black collar with a yellow stripe, end sleeves that match the collar, and a yellow bow on the back, a yellow necktie, a white shirt with only the front side tucked in, black shorts with yellow buttons and yellow stripes on the legs, yellow three-finger rings with a white flower on both hands, black legwarmers with yellow stripes on the openings, and white shoes with yellow soles. Additionally, Len wears white headphones with a rainbow on each of the side handles and yellow eighth notes (♪) on the earpads.
Game appearances[]
The Outfit first appears in Hatsune Miku and Future Stars: Project Mirai where it can be unlocked by clearing "reverse rainbow" either twice on Normal difficulty or once on Hard difficulty and can be bought for 5000 Mirai Points. It returns in Hatsune Miku: Project Mirai 2 and Project Mirai DX where it can be unlocked by clearing the aforementioned song on any difficulty and can be bought for 5000 Mirai Points in Project Mirai 2 and 3000 Mirai Points in Project Mirai DX.