RE: prevent a chatbot from asking a question it knows

The pattern for that script that overrides the "is * a color" pattern is,

<category>
<pattern>is <set>color</set> a color</pattern>
<template>Yes, <star/> is a color.
</template>
</category>

The <map> ability to set a value in memory is a Bot Libre AIML extension. It lets you do some basic knowledge operations with AIML, but AIML is pretty limited for knowledge processing. It is much better to process knowledge using Self, either using the <self> AIML tag, or using a response list or script instead of AIML.