This is something brand new to me, so here is the rookie question. I'm going to weather the Buffalo 6x6 in light sand and maybe mud do I need to paint the model first? And if so what colour would that be.?
Thanks for your feedback

Weathering is an effect that is put over the painted surface to show dirt and grime build up on the vehicle, and some wear on the paint job depending on working conditions. Paint the vehicle first. You can type in "Weathering sequence" or "painting sequence" in the search bar above and get several thread discussions that show the process step by step. Look at online builds as well as they can show the process clearly.

I assume you are talking about the Buffalo MPCV? Google images and you should get a number of photos of the vehicle. Most are in Sand. What type and brand of paint are you looking at? Spray can, airbrush? The type of paint you put on will help determine your weathering sequence and will help you get more specific answers.

First no question is a bad question if you don't know something. How else are you going to learn if you never ask.

I would always paint the model, the bare plastic usually has glossy shine to it. Even if it is the same color. Sometimes the plastic also has imprefections in it like a swirl, that need to be covered up by the paint. In addition it also provides something for the weathering to grab on to.

Most modern US armor is a sand color. Not fimilar with that vehicle but some wheeled vehicle can have additional colors on the chassis.

At the end of the day it's your model so you should enjoy it how you want. If that is unpainted plastic, I say go for it.

Thanks for the advice, That really put the light on for me.

Weathering is done to add realism and the first step to adding realism is to paint it the correct color. So, yeah, if you're going to weather, paint is step 1 in weathering.

My two cents is to highlight the order that things happen to the exterior and incorporate that appropriately on the model. Any rust or corrosion would be under the paint. The paint would be under the caked mud, and the dust layer would probably be on top of that. I have seen the masters of weathering on this forum show an area of chipped paint with the rust bubbling up, then the rust subtlety streaking down with the water direction just over the paint. If done correctly, this kind of effect is just mind blowingly awesome for its realism. I love the work and talent that is displayed on this website!

I agree on the posts prior. A painted model would always be a good starting point for weathering BUT it might not be for everyone especially if there are budget constraints. A lot of youngsters would like to go into the hobby but we all know how much funds this hobby can take. In making gundams there is an option called "no-paint assembly" which still produces great models without painting much of the kit.

Here's a reference that could give you an idea
http://www.dannychoo.com/en/post/585/Gundam.html

Going back to the topic

If you simply want to start and get the feel of making models without being overwhelmed by all the paints, washes, tools, pigments, etc. there is another option. Get a rattle can satin varnish/top coat, a tray of dry pastels from an art store and a cheap brush. I would suggest hobby top coats since I'm not familiar with how "hot" hardware spray cans are. A bottle of enamel wash would be good and cheap (tamiya panel line accent would be a start). There are a lot of videos on how to use dry pastels and scrape them to make pigments.

1. Build your model (sand off swirl marks and flat areas except for decal placements)
2. Place decals on your kit
3. Spray satin varnish/topcoat
4. Pin wash
5. Clean Pin wash
6. Apply pigments