Since Cuba is also full of brown skinned people, why would Trump want to colonize it?

It isn't as obvious as Venezuela's oil. But there are benefits to TrumpCo. Remember Tim talking about his vacations in Cuba, and the quite nice resorts he stayed at? That is Trump the God's wheelhouse. Trump casinos. Trump golf courses. Trump whore houses. The net sifter says those resorts are overwhelmingly owned by the Cuban government. Trump's quislings could sell those resorts to Trumpco, for nickles (no more pennies) on the dollar, the same way Yeltsin sold off Soviet state enterprises to his cronies.

Besides enriching himself, Trump the God would also endear himself to a Florida voting block, which is still fighting the civil war they lost 65 years ago.

it would just be providing an avenue for non-whites to legally enter the USA.

I would expect Cuba to be a de facto "protectorate" of Shinyland, as it was from 1902 to 1934: officially a sovereign, self governing country, but the US assigned to itself authority to intervene in Cuban affairs whenever it pleased. So no migration to the US, but plenty of cheap labor available to staff the Trump properties around the island.

And Cuba surely requires a massive influx of money to rebuild or modernize the Country,

Outside of the TrumpCo properties, Cubans will be given a lecture on "personal responsibility".

Steve