Color shift keying (CSK) is the only Multiple-input multiple-output (MIMO) modulation scheme supported by IEEE 802.15.7 standard. It modulates the intensity of visible lights emitted by colored Lightemitting-diodes (LEDs) for data transmission. We discuss diffierent demodulation criteria for CSK in either signal space or color space, and compare their Bit-error rate (BER) performance. In order to improve the performance of CSK, we present a coded CSK modulation scheme, which is based on the recently proposed coding scheme called Block Markov superposition transmission (BMST). For comparison, we consider Reed-Solomon (RS) code together with CSK (referred as RS-CSK), which is exploited in PHY III operation mode in IEEE 802.15.7 standard. The mutual information of CSK is also given for performance analysis. Simulation results show that the proposed scheme achieves a significant gain compared with the RS-CSK.