Color Shift Keying (CSK) is a new modulation scheme for visible light communication systems using RGB LEDs which has been standardized in the PHY III level of the IEEE 802.15.7. This paper proposes some modifications so as to include multiuser capabilities provided by a time-based multiplexing, with the modulation constellation symbols being adapted to encode data with the luminux powers of the red, green and blue color bands respectively. This is achieved by employing a simple and low-complexity time-based pulse signals structure to separate the users' data symbols, while a three-dimensional signal constellation design is merged to improve data throughput. Numerical simulations are carried out to assess the performance of this novel architecture. The statistical properties of the transmitted RGB signals ensure dimming capabilities and that the illumination function is unaffected by flickering.