Board Thread:Boruto Discussions/@comment-25319479-20160502145551/@comment-1005735-20160504230104

The tattoo is creeping on Boruto's face the pannel before, it even has its own sizzle sound effect to illustrate the fact that its spreading. Kawaki also has the same marking on his eye but both his eyes are ordinary. Logically if the weird eye is the resault of the tattoo (Or Sage Transformation as you theorize) he would also have a Byakugan-esque look to his left eye.

Besides siblings and family members have odd dichotomy between kekkei genkai all the time. Look at Haguromo's Rinnengan to Hamura's Tenseigan or Sasuke's Kagatsuchi and Amaterasu to Itachi Tsukiyomi and Amaterasu or even Sasuke's single tomoe'd Rinnengan to Madara's double Rinnengan