Hi guys,
I would like some help from you guys!!
I'm building a Vietnam dio with a M113 ACAV, OH-6 and Huey.
I need some help with some material and color range, as to do the dust and ground, which pigment colors from Vallejo is the correct one??
Thanks for now
Awaiting to hear from you soon
Ciao

For ground vehicles, Tamiya Olive Drab with a semigloss overspray is a good starting point, though some favor Tamiya JGSDF Olive Drab (which may be a better match for the late-war paint, which reflected heat better to keep the interiors cooler). If the vehicle is very dusty, you can skip the semigloss, of course.

Much of Vietnam has a distinctive red-orange soil, but it isn't everywhere, so consult color photos of your unit's area of operations. It's hard to depict this convincingly, as very few parts of the world look like that, and viewers are often startled by the vividness of the color (though the eastern USA, from Northern Florida into the Appalachian Mountains, has quite a lot of red clay).

The helicopters were finished in the lighter, warmer FS-34087 Olive Drab paint as depicted by Testors Model Master enamels. The FS-34087 paint chip in the Federal Standard FS-595a guide book was changed in the 1960's from the dark OD similar to WW2 No. 9 Olive Drab, to a warmer, lighter color, which was used on Army aviation assets after 1965 (the present Helo Drab shade replaced it in the 1970's). Changing the color chip without changing the chip's code was a source of endless confusion in the real world (and among model builders and model paint manufacturers, years later). The Vietnam-era helicopter shade was a flat finish.

Thanks Gerald for your replay!!
...but I need to be honest i get very confused

Just to ad one observation: red earth is dominant for Khe Sanh, if you want to depict that battle. I visited Vietnam some 15 years ago, and gave my best to visit former battlegrounds. Elsewhere the soil is in various shades of brown, usually with dense vegetation. Khe Sanh is currently a plantation of tea or coffee IIRC. But beware if you decide on Khe Sanh with lovely red earth, you should bare in mind that marines fought there, and that would limit your selection of vehicles and choppers.
Best regards
Marko

Short of finding a soil study of Viet Nam, you may find it useful to look at aerial photography such as is found on Google Earth or Google Maps. Or you can use colour photos whose location is clearly recorded in the caption. Like most (all, actually) countries though, VN was not issued with a specific colour of soil which stopped and started at its borders, in the same way as there is no single 'Russian earth' or 'European dust' colour. I collected three different sand samples from the coastal strip in Libya where the terrain looked basically the same.