RGB is one of the mixed multivariate signature schemes. It can resist the current known algebraic attacks against multivariate schemes. However, similar to other MPKC (multivariate public key cryptosystem) schemes, it suffers from large public key size. In order to reduce the public key size of RGB, this study extends the idea of cyclic public key to the RGB signature scheme and proposes a new scheme-CyclicRGB mixed multivariate signature system. In comparison with the original scheme, the new scheme has smaller public key size, and it is also possible to speed up the verification process. Furthermore, experiments demonstrate that it is feasible to reduce the size of public key. The public key size of the new scheme is about 40% of that for the RGB scheme. The time required for the signature verification in CyclicRGB scheme is about 60% of the time required for the RGB scheme.