How many people live there?
Have they been exploited for extractive resources?
Why do you assume everything wrong in Africa is because of colonialism??
The modern problems there are not due to colonials, but from a failed attempt at an Islamist takeover.
That's a short-sighted take on current events.
In order for a rebel group to seize power from the government, the government needs to be weak. Since its independence in 1960, the CAR has never known peace or stability, which in turn means that it lacks robust institutions and infrastructure. For almost all of it's history has been ruled by a series of warlords become dictators who barely cling onto power. None have had the resources to police more than fragments of their country, and they often abuse what little legitimate power they actually have. In this environment, rebels and bandits are inevitable. Since the country has a significant Muslim population in the north, so it's no surprise that the Northern rebels are Islamists.
I suppose we could look at that and say "well if the Central Africans had gotten their act together sooner, they wouldn't have Islamists, or would have been able to crush the rebels", but then we're immediately led to ask "why did the CAR fail to achieve the stability they needed?" The CAR seemed to get off to a good start: they had a democratically-elected government and it seemed there was going to be a smooth transition from French colony to independent country. But then their leader (Boganda) died, and his successor (Dacko) went a bit Stalin, suppressing his political opponents and squashing the democratic process even before the CAR formally received independence from France. He was deposed by Bokassa shortly after, and it all went downhill from there.
We could stop there and say "looks like the Central Africans destroyed their own democracy, so why blame decolonisation?" For one thing, France set the field of play. The CAR's territory is inherited from the French colony of Ubangi-Shari, which was nothing more than a mining and farming colony. The administrators of Ubangi-Shari had one job: get the natural resources out as quickly as possible and for as cheaply as possible. They weren't interested in building a society, so they spend nothing on infrastructure or services. The French administration didn't have to built up a robust local administration because they could always rely on the French Army if the locals tried to throw them out. The CAR's domestic government didn't have the same fallback, they had to maintain control with only the means that the French left for them. The French basically created a power vacuum.