Normally ".bg-colour", the actual class used is ".text-bg-colour" which chooses the best text colour for contrast.
This text is muted (.text-muted).
This text is important (.text-primary).
This text is important (.text-primary-emphasis).
This text indicates success (.text-success).
This text indicates success (.text-success-emphasis).
This text represents some information (.text-info).
This text represents some information (.text-info-emphasis).
This text represents a warning (.text-warning).
This text represents a warning (.text-warning-emphasis).
This text represents danger (.text-danger).
This text represents danger (.text-danger-emphasis).
Secondary text (.text-white).
Dark grey text (.text-dark).
Body text (.text-body).
Light grey text. (.text-light).
Black text. (.text-black).
White text. (.text-white).
This text is muted (.text-muted).
This text is important (.text-primary).
This text is important (.text-primary-emphasis).
This text indicates success (.text-success).
This text indicates success (.text-success-emphasis).
This text represents some information (.text-info).
This text represents some information (.text-info-emphasis).
This text represents a warning (.text-warning).
This text represents a warning (.text-warning-emphasis).
This text represents danger (.text-danger).
This text represents danger (.text-danger-emphasis).
Secondary text (.text-white).
Dark grey text (.text-dark).
Body text (.text-body).
Light grey text. (.text-light).
Black text. (.text-black).
White text. (.text-white).