Implication versus "if....then..." in written English Assume following statements are true

*

*Bob's favorite color is blue.

*Sally's favorite color is red.

*Bob and Sally always tell the truth.

I ask Bob the following question: "If you are Sally, is your favorite color blue?"
According to the definition of logical implication, since "you [Bob] are Sally" is false, the above compound proposition must be true ($P\implies Q$ is true when $P$ is false). However, the statement seems to be false as interpreted in standard written English. Is this just an unfortunate quirk of the English words used to designate mathematical implication or is something deeper going on?
 A: In English, one would say “if you were Sally“, not “if you are Sally“. We can paraphrase it as “If in some possible world you are Sally, then in that possible world is your favorite color blue?“. It’s what’s called the subjunctive mood, not the present tense. The statement is hypothetical, counterfactual, and like all counterfactual conditionals it’s trivially true because the antecedent is false. Counterfactual statements are not subject to the simple rules of propositional calculus.
A: *

*If the question was instead phrased as “If you were Sally, is your favorite color blue?” then it's natural to interpret it as “Is Sally's favorite color blue?”, whose answer is No.


*

“If you are Sally, is your favorite color blue?”

Technically, it is unclear whether “your” is pointing back at Bob or still at Sally (I discussed such ambiguity of variable recycling in this answer).


*Let's convert the given question into a statement:
  “If Bob is Sally, then their favorite color is blue.”
With the implicit premise that Bob is Sally, regardless of whether “their” refers to Bob or Sally, the above (implication) statement is vacuously true, and the argument valid, since its associated conditional $$P\to\big(\lnot P\to Q\big)$$ is a tautology.
A: (Corrections)

Assume following statements are true

*

*Bob's favorite color is blue.

*Sally's favorite color is red.

*Bob and Sally always tell the truth.

I ask Bob the following question: "If you are Sally, is your favorite
color blue?"

Suppose your name is not Sally. Then it is true that if your name is Sally (assumed to be false) then your favourite colour is blue. We say that it is vacuously true in this case.
$~~~~\neg S \to (S \to B)$
Where:
$~~~~S =$ Your name is Sally
$~~~~B =$ Your favourite colour is blue
Here is the truth table:

Source: https://www.erpelstolz.at/gateway/TruthTable.html
There is no ambiguity or inconsistency here. It's just that we have an implication $(S \to B)$ with an antecedent $(S)$ that is known to be false. Such implications are simply not very useful in daily discourse since you will not be able to use that them to infer anything about the truth value of the consequent $(B)$.
Similarly, it is also vacuously true that your favourite colour is  red.
$~~~~\neg S \to (S \to R)$
Where:
$~~~~R =$ Your favourite colour is red
In fact, any proposition whatsoever can be used:
$~~~~\neg S \to (S \to P)$
Where:
$~~~~P = $ Pigs can fly!
Though not very useful in daily discourse, implications that are vacuously true can be useful in very technical arguments. In set theory, for example, we have:
Proposition: For every set $A$, the empty set $\emptyset$ is a subset of $A$.
Proof: By definition, for all $x$, we have $x\notin \emptyset$. Therefore, it is vacuously true that, for all $x\in \emptyset$, we have $x\in A$.
