Hi Matt,
One possibility that has worked well for me is to take along some lightweight black nylon netting -- the type that is used in orchards and vineyards to keep birds out. This type of netting is very light and inexpensive and durable, and it is great for camouflaging. You can use leaves and twigs and weeds and bark and small brush and dead plant materials and whatever else is locally available and useful for camouflage: these things stick to (and can be fastooned all over) the netting, and they can create an excellent cover.
The level of camouflage attainable this way is often quite a bit better than relying on camouflage colors or paint alone; and you can also vary the colors, textures, types of materials, and levels of camouflage according to situations and local conditions.
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Another approach (it could be used alone, or combined with the above) is to use some acrylic paint to cover the yellow. Good quality acrylics will adhere well and last well, even in very lightweight, thin layers. You can also find lightfast pigments that will hold up very well in the sun. The lightfastness ratings are avaliable from the companies.
If you get two or three colors, you can use them straight and also in various combinations or mixes, to get better camouflage effects (in the natural world, colors usually come in many subtle hues and variations -- not just one straight green or brown or gray, for example, but many blends and in-betweens, differing shades and broken colors and variegated effects).
If you email tech support at
http://www.goldenpaints.com/ they will probably answer as promptly as they can; their products are of the highest quality. Other companies, such as Liquitex, also make good acrylic products; but they are often not as helpful and responsive.
Both the Golden website and the Liquitex website contain information and instructions on fabric painting, if you dig around enough. If done properly, it is quite durable. (You might want to ask them about the best procedures for this specific fabric.)
Tech support at
http://www.goldenpaints.com/ can probably provide some extra, situation-specific help via email.
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If you really want to delve into the world of mixing colors (various sorts of realistic greens for example), digging around this website will tell you more than most people might imagine there is to know about it:
http://handprint.com/HP/WCL/tech34.html
http://handprint.com/HP/WCL/palette2.html
http://handprint.com/HP/WCL/palette2.html
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[Although this site deals primarily with watercolours, acrylics can be used in much the same way, and they contain many identical pigments and colors.]