Can a creature with protection from white be targeted by a white spell that says 'target creature you control'?

Protection from a quality means the protected permanent cannot be targeted by sources with that quality. This is spelled out in CR 702.16b, which lists four effects of protection — the permanent can't be Damaged, Enchanted/Equipped, Blocked, or Targeted by anything with the protected quality (the 'DEBT' acronym). The targeting restriction applies universally, regardless of who controls the spell or what the spell does.

CR 115.4 states that a spell or ability that requires a legal target must choose only targets that are actually targetable. Because a creature with protection from white cannot be targeted by white spells at all, a white spell saying 'target creature you control' cannot legally target it, even though you control the creature. The word 'you control' restricts ownership but does not override protection.

If you were to somehow force the targeting (e.g., via a hypothetical rule change), the spell would still be illegal at resolution and would be countered by the game rules per CR 608.2b. But in normal play the targeting is simply illegal from the start — you cannot even name the protected creature as a target when casting the spell.

Concrete example: You control a White Knight (protection from black) — wait, let's flip it. You control a creature with protection from white, such as a Black Knight-style creature. Your opponent casts Pacifism (a white Aura that says 'enchant creature'), and you cast Divine Favor targeting your own creature. Neither spell can target your creature because both are white sources, and protection from white blocks targeting by any white source regardless of controller.

Note: Protection does NOT stop spells or abilities that don't target. A white spell that says 'all creatures you control get +1/+1' would still affect a creature with protection from white, because it doesn't target. Only targeted effects are blocked by the targeting restriction of protection (CR 702.16b).