Is there a way I can get Prince to make a black and white version of a colour image when generating the pdf?
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images in black and white
Not at the moment, you will need to have a black and white version of the image available (eg. created using Photoshop or a similar program) and use that.
Prince does not support the CSS "filter" property. We might be able to partly implement this property, if it is restricted to applying only to image elements. But it will take some time.
Alternatively, you can use a command-line program like ImageMagick to convert the images to grayscale before running Prince. For example:
$ convert <img_in> -set colorspace Gray -separate -average <img_out>
There is further discussion of this on StackOverflow here:
http://stackoverflow.com/questions/13317753/convert-rgb-to-grayscale-in-imagemagick-command-line
Finally, it may be possible to use JavaScript and the <canvas> element to do the conversion, but it may be a bit slow to run, so it's not the best option if speed is a concern.
Alternatively, you can use a command-line program like ImageMagick to convert the images to grayscale before running Prince. For example:
$ convert <img_in> -set colorspace Gray -separate -average <img_out>
There is further discussion of this on StackOverflow here:
http://stackoverflow.com/questions/13317753/convert-rgb-to-grayscale-in-imagemagick-command-line
Finally, it may be possible to use JavaScript and the <canvas> element to do the conversion, but it may be a bit slow to run, so it's not the best option if speed is a concern.