In a fashion show people want to see the clothes so you need white light along the catwalk. Because if you use colours these may clash with the colours in the material and turn a really nice outfit into something awful. Make it bright. You can use colours on back walls and/or when there are no models on the catwalketc . Some people use moving lights to make patterns with the music.
Fashion shows are not that hard to pull off, but they require thinking.
As cutlunch said, you need lots of white light, make sure the coverage is even, try using fresnels, S4 Parnel or ellipsoidals...stay away from Parcans if possible. I've used 4 and 8 lites before also.
The main thing is the clothes and models, that being said, go with a good white wash, and try and avoid making it extremely flat. I see that a lot, people aim the lights at 90 degrees to the catwalk, but the designers include textures on clothes, giving the lights an angle will bring those textures up, especially if the have lots of layers of clothes on. Make sure the whole of the models are lit...don't cut off their feet.
Make sure color temp is homogeneous, you may or may not want to put a CTB on the lights, depending on the type of clothing and models yuo have.
I ussually put 1 truss per side, slightly longer than the catwalk to get some front lighting angles. Also bear in mind the first 2 rows have the press and photographers, if you gotta hit the audience with lights, avoid it being those 2 or 3 rows.
I also use a front truss for the front lighting, remember the end of the catwalk is an mportant stop, an extra ellipsoidal there never hurts (that being said, make sure the models KNOW there's lights on their faces...they might walk beyond the catwalk if not it happened to me once 8) )
You may want to add a truss of toplight if you have the inventory and budget for it, but its not a vital part of the show, it helps sculpting those flat figures models are.
Movers, color, gobos, all that I ussually leave for the back wall and the model's entrance/truss warmes, etc. Avoid distracting things such as big strobes and lots of movement...the people go fo rht eclothes, not the lights.
As an off note, these things have very particular people in it...play it cool, and think and rethink what you're doing. You'll get people saying its great and people that will say the light was not flattering on a model or the swimsuit section of the show...ignore comments from the audience in these things...everyone has an opinion here.
the only fashion shows I've designed (both in college), the designers want their work to progress *through* colour and then be seen in a white light. Not a very usual technique, but it worked for their designs. Just another idea, another possibility, another way to ook at it. Good luck.