An imaging system for imaging a sample, comprising: a source assembly comprising a plurality of trans-illumination light sources (60, 62, 64) configured to irradiate an examination region of the sample with different colors of trans-illumination light; a same diffuser present in each optical path from the trans-illumination light sources (60, 62, 64) to the examination region; an excitation light source configured to irradiate the examination region of the sample with epi-illumination excitation light; an image detector configured to detect grayscale images of the examination region upon irradiation with the trans-illumination light or the epi-illumination excitation light; a processor configured to create a color trans-illumination image from grayscale images; and a first optical aperture; wherein the imaging system is configured to irradiate the examination region with trans-illumination light from each of the trans-illumination light sources (60, 62, 64) and with epi-illumination excitation light from the excitation light source without moving one or more parts in any of the optical paths from the trans-illumination light sources (60, 62, 64) to the examination region; and wherein the imaging system is configured to switch from a trans-illumination mode to an epi-illumination mode, and vice versa, without altering any optical path from any of the trans-illumination light sources or the excitation light source to the examination region; wherein the diffuser is used instead of a shutter or filter, and wherein in the epi-illumination mode the diffuser is adapted to reduce the efficiency with which the source assembly is irradiated by the excitation light source and the first aperture is adapted to block some of the scattered excitation light to further reduce coupling to the source assembly; characterized in that the imaging system further comprises a collection lens, a second aperture and a further lens; and in that the imaging system is arranged to direct the trans-illumination light on an optical path through the first optical aperture, to the diffuser, through the collection lens, the second optical aperture and the further lens, and further to the examination region in this order. a source assembly comprising a plurality of trans-illumination light sources (60, 62, 64) configured to irradiate an examination region of the sample with different colors of trans-illumination light; a same diffuser present in each optical path from the trans-illumination light sources (60, 62, 64) to the examination region; an excitation light source configured to irradiate the examination region of the sample with epi-illumination excitation light; an image detector configured to detect grayscale images of the examination region upon irradiation with the trans-illumination light or the epi-illumination excitation light; a processor configured to create a color trans-illumination image from grayscale images; and a first optical aperture; wherein the imaging system is configured to irradiate the examination region with trans-illumination light from each of the trans-illumination light sources (60, 62, 64) and with epi-illumination excitation light from the excitation light source without moving one or more parts in any of the optical paths from the trans-illumination light sources (60, 62, 64) to the examination region; and wherein the imaging system is configured to switch from a trans-illumination mode to an epi-illumination mode, and vice versa, without altering any optical path from any of the trans-illumination light sources or the excitation light source to the examination region; wherein the diffuser is used instead of a shutter or filter, and wherein in the epi-illumination mode the diffuser is adapted to reduce the efficiency with which the source assembly is irradiated by the excitation light source and the first aperture is adapted to block some of the scattered excitation light to further reduce coupling to the source assembly; characterized in that the imaging system further comprises a collection lens, a second aperture and a further lens; and in that the imaging system is arranged to direct the trans-illumination light on an optical path through the first optical aperture, to the diffuser, through the collection lens, the second optical aperture and the further lens, and further to the examination region in this order.