Hello Pšenda: thank you for your question. No, Illustrator doesn't ask which color model to use when you open. But if you open a greyscale bitmap (for example) in Illustrator, and then specify an RGB color to work with, the color displays in RGB, as does the color palette. This doesn't happen in Affinity Designer, which was what I found puzzling (until I realised you had to specify a diffeent color model explicitly).
Illustrator is a very capable vector drawing program, and it still has many really useful features not present in Affinity Designer. But I think AD may be the future of vector drawing. It has already overtaken Illustrator in some important basics (most notably node control), and I look forward to seeing it catch up with Illustrator in other areas.