I really don't understand the problem, here.
Like... what is the point of even having the options to colour, bold, or enlarge text if users are not allowed to do so?
If they want to colour their entire post, or make it big, then let them, it's their choice, and they are given the tools to make that choice. You are not forced to read their posts, just as nobody is forcing them to use "normal" text. If you dislike their post, just skip over it.
Anywho, the example that you posted isn't even that bad. Now, if somebody was posting in some obnoxious blue, that might be a bit worse, shame on those who would do such a thing.
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I'll need a therapist now.