Black is one of the rarer dominant colors in flag design, but where it appears, it’s almost always deliberate rather than decorative. In the Pan-Arab tradition, it recalls the Abbasid Caliphate. Across much of Africa and the Caribbean, it represents the people themselves, African heritage and identity made explicit on the flag rather than left as an abstraction. Elsewhere, it tends to show up in older heraldic or historical color schemes with less unifying pattern behind it.
Pan-Arab colors
Egypt · Iraq · Syria · Yemen · Jordan · Kuwait · United Arab Emirates · Sudan
African heritage and identity
Kenya · Uganda · Tanzania · Botswana · South Africa · Zimbabwe · Malawi · Angola · Mozambique · Ghana (the Black Star specifically, rather than a black field or stripe)
Caribbean heritage
Trinidad and Tobago · The Bahamas · Barbados · Jamaica · Antigua and Barbuda
Historical and heraldic use
Germany · Belgium · Estonia · Afghanistan
Oceania
Papua New Guinea · Vanuatu