It was part of the British colonial empire, but it was never really colonised. Although I suppose it didn't really even exist back then, since it was known as the Gold Coast. But the main point is that Ghana isn't a country of former colonists, it's a country of Africans, so I wouldn't consider it to be a former colonial country.
Or for a more recent example, how about Ireland? Northern Ireland was definitely colonised by the English (and is why the political situation there is messed up and has been for ages), while the rest of Ireland was conquered, but not colonised. I would say Ghana is much more like the Republic of Ireland than it is Northern Ireland.
I have to remind you that you called Ghana a colony, not me. And if you have to do these mental gymnastics to keep your definition consistent, maybe think more about it. Personally, I'm getting more and more confused by your definition and I do not know what a colonial country even is. Is it the colonizer or colonized. In my definition Ghana, India, US, Mexico, etc were all colonized. It's clear, consistent and easy to understand in my view what a colony is then. I don't need to really explain it beyond when an invader took control and ruled over a region in anyway.
Not really any mental gymnastics required. When I say former colonial countries I'm exclusively talking about countries that were founded by colonists. ie. Canada and Australia. Other countries were colonies at one point, yes, but I wouldn't consider them a former colonial country. eg. Korea was colonised by Japan, but I would NOT call Korea a former colonial country since it was founded by Koreans, and NOT Japanese.
That's why I wouldn't consider a country like Ghana to be a former colonial country, it was founded by Ghanaians. Sure, we (the UK) may have influenced their culture and that's the reason English is still their official language and they're a part of the Commonwealth, but they are still their own people. While a country like Australia would've been founded by British people that colonised the land there. They're our distant cousins.
That's also why I said former colonial countries should learn European history, because they have European origins. Australians should learn European history too, since it's literally their history. Ghanaians? They should learn their own history, if anything from Europe is relevant then sure, but otherwise they should focus on learning about their local area and history instead.