Cautious use of RGB colourspace and Photoshop CMYK preview
RGB is an obvious choice of colour space for many Photoshop users - the files are 25% smaller than CMYK files and all the Photoshop filters work amongst other advantages. However, if your file is destined for professional print rather than multimedia on-screen presentation you are going to have to convert it to CMYK at some stage - that’s where the CMYK preview comes in to save the day, the best of both worlds… you would think!
Adobe have given us the option of a CMYK preview whilst working in RGB, but caution should be taken
with this - it is as it says on the tin, its a preview. It will give you a reasonable idea of what to expect when your file is converted to CMYK but it is by no means 100% accurate and you should not trust it, you might be in for some nasty surprises if you do!
Converting your file to CMYK can produce some strange colour shifts, especially in very bright saturated colours or when exact colour accuracy is important. You should originate your file in CMYK from the start if you want to avoid issues. It is the safest option for any Photoshop Ninja working on a file destined for professional print.
Colour correction should be particularly avoided in RGB, as you can blast the colours right out of the colour gamut when converted to CMYK, producing even worse quality images than converting to CMYK from the start and loosing valuable colour information.