Does protection from a color prevent enchantments of that color from being attached to the creature?

Protection from a color grants four specific shields, remembered by the acronym DEBT: the creature cannot be Damaged, Enchanted/Equipped/Fortified, Blocked, or Targeted by anything of that color (CR 702.16b). The 'E' component directly means that Auras of the protected color cannot be attached to the creature.

This works in two ways. First, you cannot legally attach a colored Aura to a creature with protection from that color — the Aura's enchant ability would be unable to target or attach to the creature. Second, if a creature somehow gains protection from a color after an Aura of that color is already attached, the Aura immediately falls off as a state-based action (CR 704.5n), since an Aura must be legally attached at all times.

It is important to note that only the Aura's own color matters, not the color of its effects or the color of the creature it came from. An Aura that is white but grants a blue effect would still be stopped by protection from white.

Example: Your opponent controls a creature with Protection from Blue. You try to cast Claustrophobia (a blue Aura) targeting that creature. The spell is illegal because the creature cannot be enchanted by blue things, so Claustrophobia cannot target it and the cast is rejected entirely.