A dual-band dual-circularly polarized (dual-CP) multi-beam transmit-array (TA) system providing the four-color scheme at both the low- and high-frequency bands is proposed and demonstrated. The TA cells are in the form of antenna-filter-antenna structures with a reduced laminating complexity, behaving as transmissive half-wave plates. For the feeding source, a compact dual-band dual-CP array, based on a broadband stripline feeding network and four dual-band dual-linearly polarized aperture-coupled double-layered segmented patches, is designed and validated. The measured joint -10 dB impedance matching, 2-dB gain, and 3-dB axial ratio bandwidths are about 15.5% and 8.9% at the two bands, respectively, for the feeding source. The dual-band dual-CP TA and feed array are further integrated to form a TA antenna with four degrees of freedom of beamforming. Finally, two feed clusters, each containing four dual-band dual-CP feed arrays, and two dual-band dual-CP TAs – one operating at 18/28 GHz and the other working at 19.5/29.5 GHz, are integrated to produce a total of 32 beams for covering a certain area in a four-color scheme at both the low- and high-frequency bands. The dual-band dual-CP TA system is fabricated and characterized, showing a good agreement between the measured and simulated results. The demonstrated TA antenna system can be a promising candidate for point-to-multipoint communications, satellite communications, and so on.