One thing that might make sense is trying to sort them in terms of likelyhood to be distinguishable. Most users are lazy and will use the first four colors for a four player game or the like. If you make those most likely to be distinguishable you minimize problems even if you can't get a full palette of eight. For instance, the first two might be blue and yellow, which can be distinguished reliably by all three -anopias, followed by a deep red (using saturation and lightness)? I'm going off the top of my head and a couple reference pictures admittedly, but it's a start.

If it's under a different format, it should probably be saved with a different extension. .nlvl maybe?

Well that was pointless - Beat two levels rendered identical by Neolemmix changes. (Fun 6 - A Task for Blockers and Bombers and Tricky 17 - Diet Lemmingaid, or Fun 18 - Let's Block and Blow and Taxing 19 - Bomboozal come to mind)

I say  should be renamed "Emo Lix".

life is pain 

At the very least, a widescreen layout is probably a good idea. Implement the minimap from Lemmings as the rest of the status bar maybe?

Do we stick our names in the creator field, for engines that support it, or is this a 'blind' contest?

I'd probably just go to the next level - if the player is hopping around, they're going to want to use the menu anyway.