White is not considered a color when printing fine art or photographs using the giclee or digital photo printing process. An area in your image which is meant to be white will actually show in the print as an absence of any ink. That is because digital printers used for photo and fine art printing do not use white inks. Traditionally they use a combination of Cyan, Magenta, Yellow and Black mixed at different levels to achieve various colors. Modern printing systems now have adopted some additional colors to extend the depth of possible color but it is impossible to mix the different colors and get white.
So if you have a painting you want to reproduce but you used a very bright white paint like titanium white in parts of it, you will not be able to get the same level of white in a print unless the paper has that same level of whiteness.
This poses a potential problem for some artists since they want to get matching colors in their prints. To top it off, the higher grade papers for giclee printing tend not to be as bright as the lower grade papers (see my post about choosing papers for printing giclee prints).
Even though this is the case, all is not lost. Our eyes and brains are trained to take in the entire picture within context. Therefore even bright white fluffy clouds on a blue sky, printed on an off-white paper will be appreciated by your viewers.