He can't be trusted to do it himself.

"Stand up, I'm going to apply the dye," she told him.

"Wait, I can do it myself, I just need you for the bits I can't reach."

"K-T, you get Fs in art class. I already will have to go to a party with my brother's dick hanging out, I sure won't do it with you looking like a blue zebra because you can't apply it evenly."

"I'm not that bad. I can do most of it myself."

"You know what? Either you let me do it or you do it alone. That way I can say that I had nothing to do with it when everyone laughs at it and you get rejected at the door. We don't have much time until our ride to the party, your choice!"

K-T thought quickly about it. It was already insane to accept to go to party wearing this (this in this case being a bald cap and some dye), only his desire to impress Samantha with his courage to show up no matter how daring the costume assigned to him was pushing him to go forward with it. The worst case scenario would be to go through the embarrassment of doing it only to be rejected at the door, without a ride home before the end of the party, **** to wait outside or go home naked and on foot (bare too), walking multiple miles.

"OK, please do it. I don't want to ruin this."

Emily of course was simply lying, this product was designed to be fool-proof, and you could simply wash off the excess once applied with no issues, the skin being unable to absorb more than the required amount.

Using her gloved hand she began applying the dye with a sponge. She started with some rather innocuous areas like his arms and back and continued further soon there wasn't much left to do but his face, ass and crotch.

Emily was rather gleeful handling her brother's junk and giving him literal blue balls and a dick to match. She spent a lot of time making sure that the very smooth and hairless area was correctly covered. She even retracted his foreskin for him, making sure that even the head of his cock was blue. This got her some protests from K-T, but he didn't dare push it too far.

There was a reason she was extra careful to not let any of the dye on herself though. The dye was a specially designed one bought online and used for these kind of costumes for shows, but it was laced with two other liquids that Emily and her friends had bought in a sex shop. One was a watery gel than enhanced skin sensitivity, at the concentration put in the final mix any bit of his skin would soon feel like the tip of his dick, getting pleasure from a simple touch (and the tip of his cock would increase in sensitivity in the same order). The other was simply a skin absorbed aphrodisiac. Both would take around half an hour to take effect and would be harmless to anyone touching him once dry. This promised a fun evening for everyone except for K-T.

Just to mess with him, Emily then used the same sponge she just ran against his junk to do his face. He was freshly washed from his shower, but she still giggled seeing him winch.

The only bit left was his ass and Emily was really tempted to leave all or part of it undyed as part of the prank, but if K-T looked himself in the mirror and noticed it he might refuse to go to the party or make her fix it before going.

So she lathered more of the dye on his butt cheeks, massaging them in a way that would make K-T blush if his face wasn't blue. She then ran a gloved finger coated in dye back and forth in his crack, poking the tip of it at his asshole to make sure everything was covered.

The sole of his feet was actually the last uncovered bit and Emily wouldn't want to leave the work unfinished, no matter how delicate or ticklish such parts of his anatomy might become.

She had him raise his feet one after the other to deal with them.

The finishing touch was to blow-dry him for a bit and have him take another shower to wash the excess. In fact the heat from both activities would make sure the additives in the dye were absorbed faster through the skin and could better take effect.

K-T was already starting to feel really awkward when getting out of the shower and patting himself dry with a towel. It was like any change of temperature was amplified and his skin felt extra smooth and delicate. He put it on the depilatory cream from before and being exposed in such a way in front of his twin sister.

The prospect of what was going to happen at the party was even blamed in his mind for his dick starting to grow.

Emily led him outside where a car was waiting for them. She had arranged for friends of hers to pick them up in their car. (neither of the twins had a car despite both having their driving license, their mom didn't judged them responsible enough).