What to see
Two Christmas trees stand in a somewhat strange snow shower – is the colour of the two trees identical? To me the right one looks a littler darker and a little more blueish, what about you? The topic of interest here: the two trees are absolutely identical in their colour. All in all, there are only three (3) different colours in the picture.
What to do
The difference in colour between the two trees is subtle. With the pop-up menu you can switch from Snow to Bars. With the bars, the difference is somewhat stronger. You can also change all colours to your liking.
This should more appropriately be called “White's Xmas”, because it's a variant of White's illusion. There → you can find more background information.