Trimeresurus fucatus is the more widespread low-altitude version of Trimeresurus nebularis. However, both species are reported to exist on Bukit Fraser (aka Fraser's Hill), and the references that explain how to distinguish them disagree with and contradict each other. So let's just say that each of these snakes, which were found within ten feet of each other, is definitely one or the other.

The red-and-white stripes separating the sides from the bottom visible in the first snake seem to generally be considered conclusive evidence for T. fucatus, and perhaps evidence that it's a male (though maybe females have these stripes in some populations, according to some authorities).

The sharp delineation between the reddish top-of-tail and green bottom-of-tail in the second snake are often cited as evidence in favor of T. nebularis. But it seems quite surprising that the two nearly-identical species would be found within ten feet of the other (you'd expect selection pressures to have favored one or the other). And also, the second snake's eyes are definitely more yellow than green, which seems to rule out T. nebularis. So I'm just going to call them both T. fucatus.

My Travelogues and Trip Lists page includes a complete list of the herps I saw in the wild on this trip to Malaysia, as well as a travelogue of the trip.

This one also has the sharp delineation between reddish top-of-tail and green bottom-of-tail, so perhaps it is T. nebularis. But if it's T. nebularis, then that second snake above should also be T. nebularis, and I called that one T. fucatus because the first one seems to definitely be T. fucatus.

But also, some references claim that T. fucatus has more of a matte finish when photographed with a flash, whereas T. nebularis has more of a glossy finish. This snake looks pretty glossy to me (based on the extra-shiny flash highlights). On the other hand, it was a very wet night so maybe the snake is extra reflective just because it's wet. I'm soooo confused!