DISCLAIMER! Please bear in mind that rendering all the newly revealed terrain,
doodads, etc. that were ignored due to the far clip can cause a HUGE load on
your video card. So if you doubt your hardware in any way you should consider
using other alternatives such as doodads to create the illusion of your world.
Otherwise, you may

your video card.
How high is your far clip set to in your camera properties? The sky boxes are a
few thousand units out unless you are at the edge of the map. From the middle
of a test map I set the far clip to about 7 or 8 thousand to gain sight of the
sky box on a Bel'shir map. (Depending on Pitch of the camera.) ["The up/down
angle" for folks that have no experience with the term Pitch.]
If this is not your problem, then maybe the trigger doesn't work how you think
it does, or a value other that zero is needed. For example, a value of -1 in
some fields in the data editor means "all available units", not "all available units
minus one." Or maybe the game clock starts at 0.0001, not 0.0000.
Or instead of a fixed time trigger event you could try a different event to trigger
the desired action, such as map initialization.
Maybe you could mod the fog of war settings to make a blue fog, however,
having never tinkered with those settings I am unsure if this is possible.
BTW I'm Red in M:TG, so you can trust me, right pal? *with a Cheshire cat grin*
Edit: 5600 is fine for a 128x128 at a z offset of 0.5 with a pitch of 0.
Larger maps will need a farther clip though. And better hardware.
I'm rockin' an un-SLIed GeForce 8800 GT with no hiccups.
Because I can maximize the tools I'm given.
*Hits the Rig with the Monkey Wrench* "I Didn't Give You Permission To Die Yet!"