I'Am a complete newbee in the film editing world. Sorry!
How can I change the audio level for one clip and not interfere the other clips in the audio track?
A litle bit the same: how can I add color to text for only 3 text clips and leve the others without color?
Audio level: If too loud drag down the upper edge. If too low right click and normalize - or combine these two methods.
The text clips are totally autonomous - so just enter their properties and change the colour. If you copied them creating a reference to the original media then delete the clip and copy again creating a new copy where you can change its properties.