Well, you are right; this is very problematic terminologically. As described before about human vision, words of colors can mean many different things, and all that matters is the shape of the absorption spectrum; the curve of response to different wavelengths. In this case, "blue" can mean many things. More descriptive words are used such as light blue, deep blue, dark blue etc., but they are not much of help. You really have to know what you buy by checking the absorption spectrum plot.
Originally Posted by ath
I wouldn't call the plot you showed blue! It's so light. It could be light blue, but definitely not blue. But, OTOH, it is not called blue - it's called "blau 38". It is a product name that must be thought as such.