First we had Toad Sage Mode
& then it was shown Naruto’s “chakra mode” was gained directly from controlling Kuramas chakra, heightened even further after Kurama accepts him
then after that he’s able to mix in Sage Mode with it, thus Bijuu(Kurama is the bijuu here) Sage Mode
After that Hagoromo blesses him with his own form of sage mode, Rikudo Sage Mode, which is solely represented by his yellow cross eyes with no pigmentation
After that Naruto is like oh yeah let’s mix the bijuu power(Kurama + the chakra the tailed beasts gave him) with it again, with Kurama being the only one actually in Naruto, Kuramas “chakra mode”
influenced it the most which is why he’s partly his regular skin tone but still has the yellow glow rather than looking like Juubito or Godara. As well as the rinnegan + 9 tomoe on his back & tsb
After the fight with Madara, Kaguya, then Sasuke, he uses up nearly all of the additional bijuu chakra, as well as Yin Kurama.
Afterwards he now can still utilize that form with only Kurama chakra which is why he returns to being completely shrouded in yellow again but the Rikudo sage mode is still 100% there
And it’s balatantly states by Hagoromo that Naruto can contact the other bijuu through Kurama for more chakra
This is like the one thing Kishi wants to be vague about and make you put the pieces together, as well as Tobidara being real