Yes, I remember this one, took me a while to figure out. The answer is brilliantly simple. The start of your intro script is going to look something like this
titlecut [" ","BLACK IN",300]
enableradio false
playmusic "rtrack2"
2 fadesound 1
~2
titletext ["missionname", plain, 2]
~6
titletext ["text", plain, 2]
~6
_cam = "camera" camcreate [0,0,0]
_cam cameraeffect ["internal", "back"]
titlecut [" ","BLACK IN",2]
_cam camsettarget logic1
_cam camsetrelpos [-80,100,7]
_cam camcommit 0
@camcommitted _cam
I'm slightly making this up so you'll have to check all the syntax and play with it a bit, but the critical parts are the numbers that go with the titlecut commands. These are the time in seconds that it takes for the effect to happen. So at the start you ask for a fade in from black over 300s, which over the 15 or 20s of the titles means that it just stays black. Then of course you have to do a normal timed fade in of say 2s when the titles are finished.