Oakland Radio Communication Association
Pressing F8 or ALT+U enables and disables the PARTIALS window. Once you've entered at least two characters of a station's callsign, CT will display matching callsigns it knows in the PARTIALS window. Anything you see in white means you still need to work them in the band/mode you're currently working (like KQ6TW). Any calls in blue are previously worked (look at KQ6JZ).
Of course, there are many other possible call signs which start with KQ. CT just doesn't know about them. In fact the only reason why CT knows about KQ6JZ and KQ6TW is that they were previously entered as contacts. KQ6TW was worked on 40 meters, but not on 20 meters. That's why the callsign is in white.