Dull Violet-Blue vs. the Deep Blue 2 Anna

Hello. I've recently become interested in the bluish shades found in the early 2 anna settings. In The Classic Stamps of Nepal there is Setting 5 with deep blue and blue-violet, and setting 9 with a dull violet-blue. Additionally, setting 20 has a violet-blue variety. Is there any reliable way to tell the difference between "dull violet-blue" and the blue 2 anna error of color? In The Armand E. Singer Nepal 1772-1961 and beyond, it is described as just "blue." In The Classic Stamps of Nepal, though, it's referred to as "deep blue" and "dark blue." Perhaps if anyone could show me an example of the contemporary 1 anna blue that it shares a shade with this could clear this up for me. Thank you for any advice.

I have noticed that the shades for the 2 anna 1886 thin paper printings seem to slide in color from a blue or blue with a very slight touch of violet shade through various violet blue shades to finally what would be termed distinctly violet shades.  Since violet is a mixture of red and blue, it seems to me that the original blue shade might have resulted because the two anna values were printed after the one anna values by simply adding red ink to the blue ink left over from the one anna printings.  It appears to me that the red ink might have been added on a sort of trial and error basis until the proper color was achieved.  Given the low income level of the country and the general disregard for consistancy that would characterize a craft verses industrial based society, it would come as no surprise that these trial printings would simply be mixed in with the final lot of stamps shipped to the postal department rather than being thrown away.  Paper to the Nepalese printer would have not been the nearly worthless commodity that it is to us and would not have been wasted simply because the printing varied somewhat in color from the prescribed outcome.

I haver heard that Wolfgang Hellrigl is considering a revision of his Nepal Handbook. Maybe we can convince him to choose, based on the feedback of other collectors, a color guide which is easy to purchase, easy to use and comprehensive enough to cover the shades.

I mentioned it earlier, the biggest problem in naming color shades is not defining a color reference. 

Edited by Rainer

Re 2 anna blue error of colour;The best way to verify the true error is to compare with the relatively common 1 anna deep blue as often 2 anna will appear deep blue but has a slight violet tinge whereas the "true" deep blue has no such tinge. It is interesting that this error does occur in multiples and I have seen a strip of 5 but the colour was identical to the one anna