To control projection of intensity and spectral balance of color transparencies being projected on photographic paper for enlargement, a color analyzer (2) is provided which has an illuminating plane (12) formed as a screen or a groundglass, which receives a first central portion (11) the projected image from the enlarger, or at least a major portion thereof and on a surrounding framing portion (15; 31b) a reference light source, in which, prior to use with random transparencies to be printed, the relative intensities and color balances of the reference frame and the light from the enlarger have been adjusted by gray-scales, for white light, and if desired, color balance by filters (14, 34; 5; 6; 7) at a given diaphragm (D) setting of the enlarger; the same relative light intensity of frame and projected image on the imaging plane (12) is then reproduced on the subsequent transparencies, to be printed by varying the light emitted from the enlarger, for example, and preferably by changing the diaphragm setting of the enlarger to obtain the previously adjusted match on the imaging plane (12). The apparatus, preferably, is supported on a swing post (3) from the enlarger to be placed in, and out of the beam (1a) of light from the enlarger.