BTW, I think many people will be happy if the reader could colorize the chars's tone.
I know you'll answer "there are many cases", but just think about it.
Many readers do and their users are happy.
in my opinion, just need to color the tone of the current word being looked up / decided upon
thereby you avoid the compounded ambiguity of different possible word segmentations within each sentence and of tones even for a given word
... the user will choose the word variant and the characters of this single word (in isolation) can be unambiguously colored in the reader
optionally (though i would not need this) words that have already been inspected by the user and decided upon as valid can remain colored so that at the end, everything appears in color... and if we are talking about common material, colored by many users, pleco could take advantage thereof to come up with the community’s “voted” or most probable word segmentation + coloring
edit: see image for the idea