This is ASCII mode without noteye.

In some situations, colored messages will overlap normal gray text.
It's probably related to issue #3590

Character in question is an N- CK with Law skill, slaying Ancient Blue Wyrm with a bow and gaining level up in that weapon skill:
This is what I got on default color settings:

This is exactly as it appeared in the game. I guess the part about bows has been overlapped by the Law skill related message but the whole line still got the blue color tag.
There is a case where in the exact same turn, the message about burning pain in the stomach appears in the middle and further confuses the meaning, when 3 messages actually overlap in a single line - burning pains, bows level up and behaving in proper form.
What is interesting is that message log doesn't display any information about 'bows' getting a level up, but the blue color is still there.

Some screenshots attached.

EDIT: Ooops, I no longer have the save file but I think this can be reproduced with any monster in a similar situation.