We will reproduce color from your submitted photograph file as closely as possible but cannot exactly match color and density because of limitations in the printing process, monitor calibration, and image resolution requirements. You most likely won't notice this kind of color shift in a color photograph. It is more likely to happen if you pick a very rich, vibrant color for a background or some other element of your layout.
Keep in mind our high-quality commercial canvas printing process utilizes CMYK colors, unlike monitors which use RGB.
(what you see on screen)
(how printer ink may appear)
Sometimes photos can be over-saturated or under-exposed with colors based on the conversion from RGB to CMYK for printing. Also, since canvas is such a porous material it accepts colors and inks differently than flat photo paper and how your monitor represents color.