Measuring quark colour operator

[Maybe_Memorie]

What is the explicit 3x3 matrix operator which measures the colour of a quark? Essentially what I want to know is what is the analogue of $S^z$ for the measuring of spin.

 

[RGevo]

The colour charges are not distinguishable, it is therefore not possible to measure "colour projections" in the same way that one could measure spin projections with a stern gerlach experiment - is this what you are asking?

 

[ChrisVer]

the (mathematical) analogue to Sz are the 2 diagonal (commute with all the rest matrices in the repr) Gellmann matrices, but I don't think that's what you asked...