Heroes 5.5 WarGame Edition - Tactical Edition.

Giving +2 levels for building dwellings is not a good idea. Here's how it works: in the first week, we capture several cities and develop some of them (the main ones) to produce creatures, while others (secondary ones) are developed to produce gold or mana. Then, in the second week, we have the option to quickly rebuild the secondary cities to produce creatures, including top-tier ones. For example, in 3 days, we can build Angels, provided that the city level has already been upgraded to 7 (Angels require level 9). However, if we give +2 levels for building dwellings, the Angels will be available much later, which will negatively affect the development dynamics of the secondary cities. Added 6 minutes later

If it's technically possible to choose a basic color (grade) when building a structure, then this is a good idea.

No, not buildings (creature dwellings) – but specifically the forts. That is, the basic color is common for the entire city, not individual for each tier. If you need to choose a color for a creature that is different from the basic color set by the fort, then, as usual, you need to build an upgrade for that creature. One of the drawbacks of this idea is that the basic creatures in the recruitment window will be the same, regardless of the basic color chosen. The recoloring only occurs when the creatures are actually recruited (replacing the creatures), not during the preview. This may create some perception issues.