The PCT makes no express provision for photographs or coloured drawings and, furthermore, according to Rule 11.13, drawings must be executed in durable, black, sufficiently dense and dark, uniformly thick and well-defined lines and strokes without colourings. Photographs and coloured drawings may, however, exceptionally be submitted where it is impossible to present in a black-and-white drawing what is to be shown. If colours are necessary to discern details, note that these details may be lost when the image is made available in black and white in the publication and via file inspection.
PCT AG I 5.159
For further details see GL/EPO A‑IX, 1.2.