I recently purchased a printed-book from Elsevier...I was expecting a colour copy of the book, but surprisingly is only available in the electronic format....
Thanks to you both for the answers. Apparently the editor decided to publish b/w due to some “issues” in the original color images...Not convinced with the reply. Moreover, the book is not what you can could consider a cheap one.
The cost of colour printing is an important issue. The publishing department of my university uses the policy "pdf in any colours, paper in black-and-white by default". Of course, if some coloured stuff is not readable in "test print", they recommend colour printing (at a supplementary charge , of course).