Earlier quoted context omitted.
For what it's worth, my 'translation' would be, "The strong aversion to less colorful designs seems childish, and may go hand in hand with designs that treat the user as inept. I don't like being treated as inept or incapable." Seems both more likely and more charitable.
That's the same thing; "the aversion to less colourful designs seems childish" - no it doesn't. When the Queen of England wore pink, did you say "her aversion to less colourful clothes makes her seem like a child"? When someone buys a red Ferrari do you think they didn't buy a muted gray Ferrari because they seem childish? When a builder drives a yellow JCB do you think they wish for a gray bulldozer because colour i…
First, it's not that the UI is colorful, it's that many designers seem unwilling to make UIs that are monotone or subdued. That's different from disliking color for whatever reason.
The designer choosing that certain (more monotone) color schemes are not permitted could be conflated with designers making other decisions on behalf of the user, such as assuming the user would prefer fewer options for the sake of simplicity. ("Treating the user as inept")
I don't know what the OP meant exactly, but I still find your 'translation' uncharitable.
I personally like both brightly colored things, as well as more muted color schemes, depending on the situation. I don't personally think colors equate to childishness.
I can however empathize with someone unhappy that their personal aesthetic preference seems underrepresented, and feels that UI designers are making more choices on their behalf than they'd prefer.