the code you have seems to be right, However it seems to be that wlm is restricting it from colorizing.
There are some parts of WLM where even if you specify something to colorize, it simply won't. Its not because of a plus bug or anything, its just because WLM is anal and won't let it.
Another example of this is the now playing icon, even if you specify it to colorize, it won't.
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