I used three RGB images as listed below to process thru integration in APP and then finish processing in StarTools. The color was very good even after only loading the files in the Compose module.
M100 ESO VLT Optical - FORS1 B-band (Blue)
M100 ESO VLT Optical - FORS1 V-band (Green)
M100 ESO VLT Optical - FORS1 I-band (Red)