My method for the ladybird picture was even simpler. The picture was taken in RAW using the neutral picture style. In the conversion I changed the picture style - I have three that preserve red in the photo (Ruby, Perl and Only Red). These all give different effects. Ruby and Perl desaturate green but keep the other colours, Only Red keeps only the red. I played around with the additional picture styles on the Canon website before searching for more. I found the downloadable SKD picture styles on Cinescopophilia and a few elsewhere now have loads. I've also fiddled about making one or two of my own using the picture style editor.
I didn't have to do anything except swap the picture style, apply sharpening and tweak the contrast and shadows before converting to JPEG. Job done. Admittedly this method is a bit of a cheat and I already had the picture style file but it was fairly instant.