Colour conversions between CMYK and RGB use a simple mathematical algorithm and there is a 1:1 relationship between the two. Word works with RGB internally, but most printers use CMYK. Hence there is almost always a conversion going on between the two formats, but the 1:1 relationship means that is of no consequence. Choose whichever source format you prefer to work with as they're equal in terms of colour consistency.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]