Missing colours from STeP


I've written an application that imports STeP files either via OpenCASCADE (XDE) or a different library and I'm seeing something strange.

With one particular STeP file, if I import through OC, some faces have a colour, some don't; if I import it through the other library, though, all faces have a colour.

I debugged this and found out that these faces in fact don't have any specific colour per se (with both libraries).
The difference arises however at an higher level, where topological entities (body, solid, shell, etc...) have a colour if imported with the other library, while they don't with OC.
Naturally, I've got plenty of other files where OC reads the colour for those entities.

So, before I misfile a bug report, I'd like to understand: given the variety of representations the STeP format can feature, in which cases should I get attributes for TopAbs_COMPOUND/TopAbs_COMPSOLID/TopAbs_SOLID/etc...?
Is there any reason they could be disregarded with some specific file?

Thanks and best regards