How do you check that Colour is Conserved?

[DoubleHelix]

I'm asked to examine a set of processes and determine if they are possible/impossible according to the Standard Model. So I have to check that energy, baryon number, color, lepton number, quark flavor and the symmetries are conserved. I'm fine with all of these but how do you go about checking if color is conserved? I thought the colors could be assigned arbitrarily so is it just if you can't find a combination that works is it impossible?

e.g. proton + anti-proton -> pion(+) + pion(-)
ignoring the other conservation laws for now, you know (or can atleast deduce) that quark combinations of each particle (where a particle in brackets in an anti-particle or anti-color),
uud + (u)(u)(d) -> u(d) + (u)d

so could you just arbitrarily say that the colour combination is,
RGB + (R)(G)(B) -> R(R) + (R)R
and thus color is conserved

Could somebody give me an example of a process that obeys everything besides color conservation so I know what I'm looking for?

Thanks.

 

[Bill_K]

As long as you conserve baryon number, color conservation takes care of itself. It's ust a matter of picking a consistent color assignment.

 

[tom.stoer]

The observed particles are all color singulets (color-neutrality; this is different from the color confinement). This follows strictly from the SU(3) color gauge symmetry and the Gauss law constraint which enforces a color singulet condition. Colored states would transform non-trivially w.r.t. color gauge transformations.

So in order to observe color non-conservation one would first expect to find asymptotic colored states (which would violate color-neutrality individually). Second one would expect that the total color charge (of the individual states) does not add up to zero.

 

[DoubleHelix]

Thanks guys, that makes sense.