Income currency

Personally I would opt for US Dollars.  The USD to COP goes up and down but overall I think you'll come out ahead with USD.

I don't know what the tax implications are, if any - you will be a tax resident and so will be subject to the higher taxes of Colombia, either way.

Many thanks for your answer!

Then if I need to open a bank account in Colombia, would it help to have a "proper" Colombian salary in pesos rather than USD or it wouldn't matter?

Once you get a cédula de extranjería you should be able to open a Colombian bank account.  I'd then deposit some money in it because that can be handy to set up bill pay for utilities and other expenses.  But I would not deposit all my paycheck in it - I'd still take my salary in USD and change to COP as needed, while also putting some into the Colombian bank account.  It should not make any difference whether you have a "proper" Colombian salary in COP or not.

Depending on where you live and what your spending habits are you may not spend even as much as 3 million COP/month, or a bit more than $1000 USD at today's exchange rate, for all your needs including housing, clothing, food, entertainment, etc.