Reservoir delineating, which is based on a stratigraphic trap, has been successfully carried out to identify the thin layer reservoir by using Red Green Blue (RGB) Color Blending of Spectral Decomposition. The area of study is situated in the exploration zone of the West Natuna basin, Riau Province. The reservoir of this study area is dominated by the thin sandstone, which is less than the tuning thickness. The reservoir target was bounded by this two marker A3 and A4 with the thickness of 6.5 meters. Prior to map the thin layer reservoir, we applied the spectral decomposition to the seismic data by using the Fast Fourier Transform (FFT) algorithm. The extracted RGB map is extracted in the time window of 28 ms, which is synchronized to the dominant frequency of the seismic data, to illustrate the isofrequency. The selection of isofrequency is based on the time-frequency where the high frequency is defined as 45 Hz for the red color, the mid frequency is 30Hz for the green color and the low frequency is 25 Hz for the red color. Our interpretation was performed on the RGB blending map to delineate the stratigraphical trap that was mostly dominated by the channel sand.