They are the color of the old photograph. This is to emphasize , no doubt, the fact that they are themselves a painting, flat and lifeless.

How do you classify the 'to do' above? One of those used as the complement of a clause, as in 'The main thing is to stay calm ' ? Or one of those 'be to', which is used to state strong expectations, as in 'The President is to visit Japan' ?
Hello Taka, good to see you.

I would take the to-infinitive here as the subject complement.

Students: Are you brave enough to let our tutors analyse your pronunciation?
Not sure if this is where you're going with your question, but it's neither of the two you mention, in that it is an infinitive of purpose. "This (the color) is [in order to emphasize / for the purpose of emphasizing] the fact that ..." The "in order to" paraphrase cannot be used in either of the two examples you mention.

Thank you, MrP and CJ.

'In order to' ! I didn't come up with such a smart idea!!