The Wizards Rainbow
The Wizards Rainbow was introduced in Wizard and Glass and this is how it is currently understood. There are 13 glass balls, one for each of the Twelve Guardians and one for the Black Tower. Rolands father refers to them as Bends in the rainbow. The Bends are identified by color in two sections, the first when Roland is talking with his father just before leaving for Mejis and the Outer Arc, and the second when the ka-tet are standing in front of the glass gate. Those identified are the Pink, Black, Blue, Green, Orange, Yellow and Purple. The only color that is associated with certainty is Black which stands in the middle of the Rainbow for the Black Tower.
It could be seen, in hindsight, the Pink Bend previewed in Blaine the Mono. If this is the case, the Bear would most likely be the Guardian associated with the Pink Bend, however, the Green Bend, according to Roland's Father, is reputed to be in Lud, therefore, the Bear could be either Green or Pink. The Orange Bend was last known to be in Dis, and the Blue was last seen with a band of Slow Mutants, however, they lost it around 63 years before we first meet Roland on the trail of the Man in Black.