Banners generated with command having a black base

What is the exact command you are using?

Works as intended: Default banner (from /give user banner) is black.

Just as example, but I've tested it with various designs and colours.

/give @p minecraft:banner 1 0 {BlockEntityTag:{Base:2,Patterns:[{Pattern:cbo,Color:12},{Pattern:bts,Color:15}]}}

Why would this be as intended? If it is working as it's supposed to, rather than being a bug, then I recommend a change.

You need to use the data value.