Red, green and blue (RGB) are the primary colours of light. Blue, red and yellow are the primary colours for pigment. Professional printing services use CMYK (cyan, magenta, yellow, k is for black). Before sending your big photo project to the printer, convert your images from RGB to CMYK on your computer and adjust them accordingly. You will notice a difference since CMYK has a smaller colour gamut than RGB.
Did you know that Adobe RGB has a greater colour gamut than sRGB, which has a greater colour gamut than CMYK? Adobe RGB > sRGB > CMYK
Adobe RGB colour gamut (original image)
Image converted to CMYK