The "Big Hero 6" toys released a new line titled "Big Hero 6 Stealth" and its hues of blacks and greys caused speculations and theories that the Big Hero 7 sequel will be darker than its forerunner.

Japanese toy maker Bandai released the "Big Hero 6 Stealth" which dropped the very colorful theme of yellows and reds in favor of blacks and greys. All action figures from Baymax to Fred are painted with heavy black hues. This theme may actually hint a dark tone for the sequel.

Ever since Stan Lee's announcement that a "Big Hero 6" sequel will happen rumors started to circulate online. Most of them point to the possibility that Tadashi is alive. According to reports, Tadashi would make a comeback as Sunfire, a member of the Marvel Universe superhero team. Sunfire is an original member of the team and has a power that absorbs heat and converts it into plasma.

Tadashi is likely to appear as a villain in Big Hero 7 and the theme may be hinting Hiro's struggle to fight his adored brother. A fight between the two brothers certainly looks to be dark and emotional, that a less lively colored costume is necessary to reflect the overall theme.

In the Marvel series, Sunfire ended up joining the team, so speculations abound that in Big Hero 7, Tadashi would also have a change of heart and will end up joining his brother. In "Big Hero 6," it was shown how Hiro looked up to his big brother, Tadashi, who died an unfortunate death and left the little brother to continue on his legacy.

A theory of a crossover with X-Men is also buzzing since Tadashi as "Sunfire" was part of Professor X's team. And since both properties are currently owned by Disney, this is a perfect opportunity for Tadashi to show up in the Marvel universe. The D23 Expo in Anaheim Convention Center is a few days away and Disney might reveal any updates on the sequel.

"Big Hero 6" was dubbed as the highest grossing animated film last year. The movie made $652 million worldwide in addition to winning the Academy Award for 'Best Animated Feature.' The sequel, "Big Hero 7″ is likely to premiere in 2017.