The apparent contrast in colours is misleading.
'A black box' is a metaphor for something that can be detected but not understood.
A blueprint (based on an actual paper plan) is a definition.
The sentence seems to me pretty silly - looking for a clever bit of wordplay and ending with nonsense. There could in principle be a blueprint for treating cancer, but I think we'd have heard if anyone had found it; in any case, cancer itself would not be the blueprint.
But what the sentence means is that cancer has gone from being an unknown menace to be something that is to some extent understood.
b
PS There's another meaning for 'black box' but this is irrelevant - it is a flight recorder, and I understand
it is usually orange!