[Aavso-photometry] Color Index for Transform

[Massimiliano Martignoni]

Dear Friends,
recently I started CCD photometry of variable stars using B V R I filters.
I find the transformations coefficients (T) for each filter using the AAVSO 
(Cohen) procedure, after I apply (T) to my instrumental magnitudes using 
the well-known formula: M = m+T(CI).
First and second order extintion are not important for my question and are 
here omitted from the above formula.
My problem is about the "right" Color Index to use.
Are correct the following equations?

M(B)=m(B)+T(B-V)
M(V)=m(V)+T(B-V)
M(R)=m(R)+T(R-I)
M(I)=m(I)+T(R-I)

Thank you very much in advance for any help!
Sorry for my poor english...

Massimiliano Martignoni
Milano, Italy