Find minecraft colour codes in string
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Your code returns false for the message &quot;hello&amp;9&quot;, because the method doesn't check the last character. Change the condition in the for-loop to message.length() - 1.

An alternative is to use a regular expression:
public static boolean isMessageColoured(String message) {
    return message.matches(&quot;.*&amp;[a-f0-9].*&quot;);
}

This regular expression matches at least one occurrence of &amp;[a-f0-9] in the message.