The essence of Force clouding, as it’s explained in the Legends timeline, is that it’s more of a constant act of concentration than a spell you cast (except sometimes — we’ll get to that). Jedi are able to feel other life forms and energies through the Force, as everything is connected. The Sith technique was basically a projection, putting forward an energy signature that blended in with the background noise and masked the dark side energy of the Sith in question. Doing this over an extended length of time required both substantial power and delicate focus. The fact that Palpatine successfully maintains the charade for so many years is even more impressive.
In “Darth Bane: Rule of Two,” a deeper form of Force clouding is introduced, by which a Sith could project not just a neutral image, but one of light side power. This technique, hiding the user as a Jedi, required a more in-depth use of arcane Sith magic.
The transformation that Palpatine undergoes in “Revenge of the Sith” is likely due in part to the release of this spell. He can finally stop masking his true form and focus the full brunt of his energy outward. This doesn’t explain how he’s able to prevent the Jedi from seeing the future, though.
