Color-luminosity diagram of Cyg X-1 and other black hole X-ray binaries from the RXTE archive. The transient source GX 339−4 shows a q-shaped pattern, while Cyg X-1 only populates the lower branch of the q. The soft and hard bands are 1.5–5 keV and 5–10 keV, respectively, and the color is derived from (absorbed) fluxes of phenomenological model fits. The NICER data (red diamonds) cover the entire color range seen in Cyg X-1 with RXTE. Red circles with a plus, times, and minus sign within it denote NICER observation 2636010101, 0100320110, and 1100320122 of Cyg X-1, respectively. The blue pentagon and green triangle denote NICER observations 1200120268 of MAXI J1820+070 and 2200530129 of MAXI J1348−630, respectively.