As the Cape Colony, in my game only Food buildings ever show up as predicting to be profitable, so I'm not sure what to build.
Also after a few years from the start date, only my new colony with 1k dudes is being listed as the only place any building is expected to be profitable, but after building something there the new factory ends up losing money immediately...
I'm completely unsure how to grow since Importing anything is useless, with the UK always taking the majority of things I need imported, and the building profit prediction seems broken.
I've found so far that the building predicted profitability tooltip is the most useless thing in the world and should be ignored at all times. I don't think a single building I have built/levelled up in my first (tutorial) game as Chile so far has ever once indicated it would be profitable - and yet almost every single one of them is and the couple that aren't still go through intermittent periods of profitability.
Instead I've found it is much more effective to simply use your own judgement as to what you think would make a profitable building (e.g 'this good is really expensive in the market, I should attempt to produce it'). A lot of the time I do end up with buildings which are initially unprofitable, but I'm able to make them profitable by switching around production methods in other buildings to cheapen the input good costs etc, or increase demand for the unprofitable good by seeing if it can be used in other buildings' production methods or exporting it and so on. I sometimes find myself pre-empting demand as well by building initially unprofitable buildings (like a paper mill) which I know will become profitable once my next building finishes which needs that good (e.g the bureaucracy producing building, I forget its name).
Not all of this is applicable if you are in the British Market of course, as that provides you with an incredible amount of goods at your disposal by default as I understand. I haven't played as a nation in that market myself, but from what I see the general strategy appears to be to invest heavily into buildings that produce whatever is in high demand in the British market - and you don't need to waste time & money diversifying out your buildings and producing most everything you need like I've been attempting with Chile because the market is already providing a lot for you.
TL;DR: Ignore the predicted profitability. I have never seen it be a useful metric thus far - I was actually considering making a thread about it. The only times I have ever seen it be useful is when changing production methods - it sometimes gets that right.