There are many reasons why contemporary botanical artists like me paint from real live specimens and not from digital images or photographs. There are of course the traditions and the history of the genre to be respected but, in addition to that, there are practical reasons for painting from live specimens.
One of those reasons is colour accuracy. There’s no question that the colour of a live specimen cannot be anything but what you see. You’re not seeing an interpretation of the colour of the specimen, it is the colour of the specimen.
On the other hand, when you see the colour of a specimen on a digital device, it is an interpretation of the real colour by the camera and the display of the device in question. And different devices interpret colour with varying degrees of accuracy. If you have any doubts about this, just see the image below. But if you need further confirmation of this phenomenon, simply photograph the same specimen in the same conditions (same light, same magnification, same angle etc.) with four or five different devices. Put them side by side, and you’ll have four or five different colour interpretations.
In the case of a photograph, the interpretation is affected further by the printer. Different printers will print the same photograph differently.
In other words, if you paint from a digital image or a photograph, your interpretation of the colour of the specimen is an interpretation of the camera’s interpretation of the colour of the specimen.
Interpreting and capturing the colours of a live specimen accurately (we strive for accuracy in botanical art, remember), is hard enough without starting out with an already distorted colour interpretation.