Joy and Irene scalped >>>>>>
It definitely looks like a dual concept going on these teasers.
Wendy's image was obviously a leak or pre-teaser, since Joy and Irene's teasers are themed on their official colors, green for Joy and pink for Irene.
Seulgi has orange hair so she'll get the orange/yellow theme to match her color probably. Interesting that SM has kept their Happiness colors even now.