Registries are notorious for getting colors wrong and I would never take their word as 100% on a color. The JC in particular, consider the fact they register greys as "roans" on a regular basis. There are many, many misregistered horses out there. Registries are not current with color genetics.
Black based horses can and do sunbleach. Some blacks will and some blacks wont, and some blacks will sunbleach to various degrees.
MN - Here is the link to the only place that tests for brown. Pet DNA Services of AZ - Equine Services