Actually, it doesn't look too high-res. I'm looking at the Highland screenshot on the left. The green blocks at the bottom are ~16x16 pixels, which is exactly the size I was expecting. I can therefore assume that the screenshot is to scale, and when I did a quick botch job of superimposing it onto a Lemmings 1 screenshot, it fits quite nicely (see attachment).
As for the colours, I can't tell. The image is badly smudged by JPEG compression. However, like in the first game, I think there was a lot of dithering to give the illusion of more colours than there actually were.