I think this phenomenon should be looked at from a wider perspective. If you flick through the large-plant images, you see that blue is used a lot in certain smaller plant parts. Seeing how often blue is used, I am almost certain that it is not literally blue but perhaps some catch-all shade for "dark color bit" or "bit that turns dark when dried".
They don't use black in the plant drawings, and brown is reserved for woody parts and some leaves. Hence, I think that the color is relevant but shouldn't be taken at face value.
Just an example of a bit that turns dark when dried. This is clove as it looks on the plant (looks extremely Voynichy)
![[Image: 2.3.12cloves2.jpg]](http://www.brittanypowell.com/wp-content/uploads/2012/02/2.3.12cloves2.jpg)
And clove in its dried form:
![[Image: 437389_womenw.jpg]](http://almraah.net/uploads/11-2015/437389_womenw.jpg)
They don't use black in the plant drawings, and brown is reserved for woody parts and some leaves. Hence, I think that the color is relevant but shouldn't be taken at face value.
Just an example of a bit that turns dark when dried. This is clove as it looks on the plant (looks extremely Voynichy)
And clove in its dried form: