i want to start painting my miniatures, but i dont know how to go about painting the "master" monters (the red ones) can someone please tell me how i could paint these ones? i already know that i could just distunguish them by leaving the bases red or white, but they might be too dark for the paint.

If you use a black undercoat for painting the red ones and leave the normal ones as white, you'll end with much darker tones for the masters.

then should i paint with lighter colors for the masters?

I'm not really sure. I've never painted plastic miniatures, just metal ones. On metal ones I'd use a dark undercoat and then dry brush the actual colors on, using different color schemes to differentiate between different types. Assuming dry brushing works on plastic the same as it does metal, the white base of the normal minis should serve to make them much brighter looking after dry-brushing even if you use the exact same colors.

I'd still leave something to differentiate them though (maybe just leaving the red bases on the masters?). Even if a black base vs. white base gives a noticeable difference, if it's not noticable at a glance you'll want more. Otherwise you end up having to peer across the table several times to see which mini is which.

Check out the pictures on Boardgamegeek as there are lots of pictures and examples of paint jobs. For mine, I went with two indicators for the masters. They have a red ring around the edge of the base. Also, if there was any clothing on the figure, I painted it some sort of red. Just be creative and look at each figure and figure out something that will help you tell them apart.

THANK YOU ALL, i think you answered my question for the most part

There are lots of examples of painted minis here:

http://new.fantasyflightgames.com/edge_foros_discusion.asp?efid=4&efcid=1&efidt=11914

Including mine.

I painted the bases for the masters red, and the normal monsters grey. I also painted the masters in similar colour schemes, but varied the actual colour tones a little.

For example, the Bane Spiders:

I gave the body of the master an extra wash of red to make it stand out more, and put an extra circle of colour on the ey reflections to make them brighter.

The master Dark Priest had a red wash added to his robes, over the brown the normal monsters recieved, and had his censer painted gold rather than silver:

The base colour makes the figure type clear. The extra layer of colour or a diffently painted robe or hair colour, will then make the masters stand out.

One thing I did when I painted mine was to read the creature descriptions in the rules as they usually offer some direction as to ways of painting the masters differently. But honestly it really comes down to your own personal taste as to what kind of paint scheme they get. Just be sure that all normal monsters looks close to identical in their paint schemes and the Masters to theirs so you can tell them apart. But BGG has lots of options as to how others have done this.

I didn't like the idea of a red base so I painted a good portion of the master mini's with red.
Master Beast Men would have red cloths and the others would not have any trace of red on them. It's working out well. It's very easy to tell them apart.