Gearbox Software is adding a colorblind mode to Borderlands 2 as part of an update planned for all versions of the game. Programmer Jeffrey Broome wrote a blog post covering his research into color vision deficiency more generally and what to expect from the mode.
The main issue for Borderlands 2 has to do with the way color is used to indicate an item's rarity. The studio's solution is to add a simple text indicator on item cards that say the color (e.g., "[Orange]"). This will appear for all items whether they're dropped in the world, are inside a chest or vending machine, or are being viewed from your inventory.
Not an ideal solution but it should get the job done. Once patched, Borderlands 2 will offer its colorblind mode in the Video Options menu with three types of vision deficiency selectable: Deuteranopia, Protanopia, and Tritanopia. It'd be nice to see this offered as a standard option for gamers but it's a welcome addition nonetheless.