of one or more continuous intervals of data (called observation intervals) separated by earth occultations. Each observation interval has a maximum duration of $\sim$1 hour per interval. Our database contains a total of 349 observation intervals. For each observation interval we produced light curves with 1 sec time resolution in three PHA channel intervals: A:0-13 (2–5 keV), B:14-35 (5–13 keV), C:36-255 (13–60 keV) (energy conversion corresponding to PCA Gain epoch 3). We subtract a constant background level of 10, 20 and 100 cts/s in the A, B and C bands respectively, as determined from the analysis of typical background spectra. Although this is only an approximation, the high source count rate minimizes the effect of background variations. From these light curves we produced a total light curve (R=A+B+C) and two X-ray colors: HR$_1$=B/A and HR$_2$=C/A.

The analysis described below is based on different combinations of these three parameters, R, HR$_1$ and HR$_2$. The choice of the definition for the two X-ray colors was made to ensure the linearity of the resulting color-color diagram (CD): any linear combination of two spectral models lies on the straight-line segment connecting their locations in the CD.

The energy spectra of GRS 1915+105 are usually 