Onion SKin activation issue

Hello, I can’t seem to be able to turn on the onion skin, I’ve seen people showing it active with the lateral squares to the layers numbers (in the onion skin panel) turned on but mine keeps being grey.

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Hi toto

While it may not seem obvious, the icons on the left are buttons too. Those buttons toggle onion skinning for previous and next frames.

The buttons on the right control whether the onion skin will be colored with red and blue.