Hi Andrei,
I have done many batches of the germn of this species. They are all very predictable and show their colors early. Here are some pix for your ref.
At about 2 mths old, the upper surface of the leaf will start to have faint Maroon blotching. It takes only another week or so for it to be apparent.
At 4 mths, all the markings are very distinct. The bottom of the leaf is a beautiful semi gloss Red in color. The mid rib and the p-stem have also turned Red at this stage.
Unless you are very lucky to get sds of the
M-a-s-sumatrana Var concolor which is all green, then you may have something else on your hand.