A/C with PAG: how to charge with dye?

[Konstantin Bogach]

Hi.
I am going through retrofitting.  Right now everything is off and open.
Yesterday I put compressor together after changing gaskets turned into
complete disassembling as I dropped one semisphere-like rocker.  One of
those which sit on a piston.  I will charge A/C system with PAG.  My
question is:  what kind of product should I buy to add dye?  I don't
want to mix with ester oil.  I've read that dye is mixed with oil in can
(no info on the can I saw).  I think it is ester oil.  I also saw a can
of R-134A with dye which says that it should be charged liquid.
Instruction says that you can not charge liquid via low side  - can blow
up.  It sould go first trough a throttle.  What is throttle?  Is it
regular valve which used for R-134A charging?
Is there dye in the free form which I can just add to PAG oil before
adding oil?

Thanks.
Konstantin.