Canon 550D - Manual (Page 76)

A Selecting a Picture StyleN
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S Neutral
This Picture Style is for users who prefer to process images with
their computer. For natural colors and subdued images.
U Faithful
This Picture Style is for users who prefer to process images with
their computer. When the subject is captured under a color
temperature of 5200K, the color is adjusted colorimetrically to match
the subject’s color. The image is dull and subdued.
V Monochrome (C: Monochrome image)
Creates black-and-white images.
W User Def. 1-3
You can register a basic style such as [Portrait], [Landscape], a
Picture Style file, etc., and adjust it as desired (p.91). Any User
Defined Picture Style which has not been set will have the same
settings as the Standard Picture Style.
Other than with 1, the black-and-white image cannot be reverted to
color. If you want to later shoot pictures in color, make sure the
[Monochrome] setting has been canceled. When [Monochrome] is
selected, <0> will appear in the viewfinder.