VDUs use additive colour and hence the RGB colour space - if you add Red Green and Blue light together you’ll get white.
Printing uses subtractive colour and hence the CMYK colour space - if you take black and remove Cyan, Magenta and Yellow from it you’ll get white or conversely if you take a white sheet of paper and overprint Cyan, Magenta and Yellow then you’ll get black - well actually in practice you’ll get a dirty grey which is why the 4th black plate is used to overprint the black.
Why this digression … ?
Com apps like browsers are designed to operate on VDUs and therefore use the RGB colourspace. Some like Photoshop will provide an approx rendition of CMYK, others like my version of IE6 won’t. Thus when I downloaded your CMYK jpg, IE gave me a nice red cross but when I converted it to RGB, IE showed it in all its glory.
As regards file size - a CMYK jpg will always be bigger than its RGB cousin because it has an extra channel - 4 instead of 3. In the case of your pic etv1_cmyk is 44,688 bytes and etv1_rgb is 22,996 bytes at exactly the same pixel size. That’s why photo library CDs, although intended for print (CMYK) use are always in RGB format - because they can fit more pics on a disk
