Unlike in the manga and most other media, Seto Kaiba had green hair in this series.
His appearances in this series are based on his appearances in "The Cards With Teeth" and Death-T from the manga. Additional aspects, such as The Four Game Masters are also added and various events changed.
Kaiba is nearly identical in appearance to his manga counterpart except he has green hair and yellow eyes in this series. The Toei's version of the anime run for the first time in April 1998, while the fourth volume of the manga - Kaiba's Revenge - was released September 4th in 1997. In that fourth volume, Kaiba is clearly depicted as having brown hair in one of the color page of the Chapter 27.
Death-T was a "theme park" created by Seto Kaiba in-order to kill Yugi Mutou. He made this after he tied his first duel with Yugi Motou. Kaiba invited Yugi and his friends to the Death-T theme park. When Yugi arrived, he found out that Kaiba's men had kidnapped Yugi's grandfather, Sugoroku Mutou. He then challenged Yugi's grandfather to a Duel, which Kaiba won. He punished Yugi's grandfather with a Penalty Game, creating virtual holograms of 3 "Blue-Eyes White Dragons". Solomon received too much of a shock from the holograms, rendering him unconscious.
Yugi swore to avenge his grandfather. He had to battle his way up to the top levels (Death-T 4 and 5) where Kaiba was waiting along with his brother, Mokuba. Yugi managed to get to the top level, but before dueling Kaiba, he had to defeat Mokuba in a game of Capsule Monster Chess. Yugi won and then started his Duel with Seto Kaiba. He managed to defeat Kaiba with the five pieces of "Exodia". As a Penalty Game for Kaiba, Yugi shattered his evil soul using the "Mind Crush" Penalty Game.