Use Nikon or Canon.
The Canon 100-400mm zoomm is good for day-time with plenty of ambient light.
The Nikon equivalent is the 80-400mm zoom or their more costly 200-400mm zoom which is more bulky, far more costly, but also better at night as its maximum aperture is f4.
Having said that, there are numerous options, including independent (after-market) lens brands such as Tamron, Sigma and Tokina.
Canon telephoto lenses (the L-Series upmarket ones) are usually white in colour. Nikons are black. Canon claims that heat can adversely affect black lenses in daylight, but their distinctive white lenses are also a branding/advertising thing.
Some surveillance and paparazzi photographers in Los Angeles are said to use (white) Canon lenses in the daytime and (black) Nikon gear at night. However that would be costly and really depends on what you are doing/photographing.
For camouflage, there is really only one superb option: take my advice and go to
http://www.lenscoat.com :wink: and in crap weather go to
http://www.aquatech.net for rain covers, if needed.