Egypt was brown and black. Babylon was brown and black. The Hebrews were brown and black. Persia was black and brown. The Moore who ruled Europe were black and brown. Carthage was black and brown. Mensa Mussa 'discovered' America before Columbus, who said Blacks existed in Americas. Also, Pacific Islands.
If by black as I suspect they are making a point about sub Saharan Africa civilisations they were until the European colonisation mixed between tribalism and the early iron age and generally quite disconnected from the rest of the old world making it quite difficult to contribute to the rest of the world, there are a variety of factors behind this mainly lack of navigable rivers and few beasts of burden available for the majority of history (these limit communication and thus spread of ideas).
Carthage was definitely not black, they were Phoenicians which are a Semitic group of people. I've have seen a lot of historical revisionism online in regards to which civilisations were black but ironically it would make no difference if they were for the people who typically make these claims (African Americans usually) as they would not descend from them anyway so it's hardly a point to draw ancestral pride from.
Brown is such a broad brush it's not funny basically everyone not from Northern Europe aka white and not from Sub Saharan Africa aka Black. By that measure I would say it's pretty even but a fairly silly point as advancements from Europeans in the modern era from shaped the whole world and allowed it's population to explode by many magnitudes including allowing the African population to go from 10's of millions to 1.4 billion today likely to peak in the range 2.5-4 billion arguably the biggest benefactors of European scientific endeavours.
I would like to make the final point peoples level of Melanin is not a basis for id groups as it can vary over time, there were no white people 10000ish years ago it's a rather recent adaption to the northern climates of the planet you see similar skin lightening in east Asians vs south east Asians merely an adaption to UV levels in the given location.
No race has contributed more or less to history then others, we're just being taught more minority history in school, however when you do the research we've all contributed to the world. In fact Caucasians found out how to use electricity and invented the internet. So if your claiming that minorities have done more then Caucasians you might want to take a look at the history behind your monitor.
I understand the desire to honor one's ancestry. But to start to define how one group of people contributed more to the human race is purely supposition and speculation. Every civilization/ethnicity has contributed to human race. How do you even begin to define "contribute to history" and which contributions outweigh the other? Where do you even begin?
Was it the ancient Greek's with their quest for knowledge and philosophers? Perhaps the ancient Chinese who invented gunpowder, paper, printing, and the compass? Maybe it was Japan who their inventions of pottery, mass media, the novel. Perhaps abacus which a like the modern-day calculator. Was it America with its Apollo Lunar Space program, the cell phone, the computer. Maybe Europe with the mouldboard plough, the mechanical clock, penicillin, and eyeglasses. Africa with the discovery of mathematics, mining of minerals, with Ethiopia having first recorded Laws, ancient African philosophy.
I guess my point is that every nation of people has contributed to the advancement of mankind. That it's all interlocked like a chain, to say anyone link of the chain is not important, is not understand dependence of each individual link has on the other.
Last point, as near as I can tell, brown is not an official classification of ethnicity. Definitely not used by US Office of Management and Budget, and the US Census Bureau.