Is there any benefit to sticking with the same color, Pokémon Black > Black 2 and Pokémon White > White 2?
The sequel is designed so that if you had the old Black (Reshiram) and get Black 2, you will get the same exclusives (not excluding the new non-Unova Pokemon) as the old Black with the exception of getting Zekrom instead of Reshiram and vice versa for White and White 2 (Reshiram instead of Zekrom).
In other words if you get the same color, you will be able to get the opposite legendary and have the same exclusives, but if you get the different color you'll get the same legendary as your other game, but different exclusives.
Black 2 Exclusives
- Magmar
- Sudowoodo
- Heracross
- Magby
- Plusle
- Volbeat
- Spoink
- Grumpig
- Registeel*
- Latios
- Buneary
- Lopunny
- Bonsly
- Magmortar+
- Cottonee+
- Whimsicott
- Gothita
- Gothorita
- Gothitelle
- Vullaby
- Mandibuzz
- Zekrom
- Black Kyurem
White 2 Exclusives
- Mr. Mime
- Electabuzz
- Pinsir
- Elekid
- Skitty
- Delcatty
- Minun
- Illumise
- Numel
- Camerupt
- Regice*
- Latias
- Mime Jr.
- Electivire
- Petilil+
- Lilligant+
- Solosis
- Duosion
- Reuniclus
- Rufflet
- Braviary
- Reshiram
- White Kyurem
*Obtainable in both versions via Unova Link
+Obtainable in the opposite version via in-game trade.
Certain areas will have aesthetic changes between the two versions, such as Route 4, the cave the connects Yamaji Town and Undella Town, and Opelucid City.
Fes missions will differ between the two versions and Join Avenue will sell different items depending on the version.
Although Black City and White Forest are exclusive to their respective versions, you can use Unova Link to switch between the two.
If this game is similar to the Japanese release then yes there is a benefit, because White will have Reshiram instead of Zekrom, and black will have Zekrom instead of Reshiram, so you will have both legendarys if you trade over your old legendary.
Hope this helped!