Question

Is V the reference vector for parallel RC circuits?

Answer 1

Yes.

See below

Explanation:

I

In any parallel circuit of elemnts: R,C,: resistance, capacitance (and or inductance) , the voltage across all 2 elements is the same, the current through individual elemnnts and its phase differs.

Since the voltage is the common factor, the vector diagram will have the 2 currents relative to the voltage reference vector.