In an upcoming, undated update Borderlands 2 will be introducing a new option for players with color vision deficiencies to make the game more accessible. The new colorblind mode will address three different types of colorblindness (Deuteranopia, Protanopia, or Tritanopia) in order to make it easier for colorblind players to differentiate between normal and rare loot, which are marked by colored beams of light. When the mode is enabled a color tag will appear on the first line of text underneath the stats in the pop up on loot (see below).
When the update is released, colorblind mode can be found and activated in the Video Options menu.
According to Jeff Broome, there is a bug when colorblind mode is set to protanopia causing red and green to look similar to protanopes. Broome states that the bug will be fixed in a future update.