Ever since I started colouring with watercolours, I've had trouble scanning them properly. Most scanners I used would suffer from highlight blow-out. The sometimes very detailed changes in colours and intensity would vanish.
By chance, I got to try out the scanner on a Canon Pixma MP540. I set it to 'photo' for the scan (I always do if the scanner has the option) and to my surprise the scan looked very good. It still differs a little from the original but it has that same amount of nuance in colour, and only required a teensy tweak in contrast to make the colours pop. On the left the image from my other scanner, it suffers from highlight blow-out. The second one looks much better.