When you convert and image from one ICC profile (Color-space) into another ICC profile there are generally some colors that one color space is incapable of reproducing. This is very common when going from your source ICC profile (Adobe RGB or SWOP V2 for example) to your printer ICC profile (your printer profile, 720v Epson Premium Luster for example). Since your source ICC profile is larger than your printer profile a rendering intent is used to shrink/map the source ICC profile to the printer ICC profile. The three main rendering intents are Perceptual, Relative Colorimetric, and Absolute Colorimetric. For recommendations of which rendering intent to use click here.