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Each member in the fermion generations has its own anti-particle with opposite electric charge and/or colour charge, e.g., the anti-particle of electron is the positron with one unit of positive charge and identical mass.
The electric charge for quarks appears to be either -1/3 or 2/3. However, when three of them combine to form a baryon (fermion affected by strong interaction); it is always in such a way that the total charge is +2, +1, 0, or -1. When a quark and anti-quark combine to form a meson (boson affected by strong interaction); it is always in such a way that the total charge is +1, 0, or -1.
Each quark can carry either one of the three varieties of colour charge -- red (+1/2), green (-1/2), and blue (0). This is just a label (a name) and has nothing to do with optics. In order to form a baryon the three quarks must each carry a different colour to add up to white (0). While in a meson the colour would be balanced by the anti-colour (such as red and anti-red).
The force carriers are gauge bosons, which mediate the various kinds of interaction between the fermions. While photon does not carry electric charge, the gluons and the W bosons do carry colour charge, and electric charge respectively. The range and relative strength of these force carriers are indicated at the right in Figure 15-02.
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