Actually there are three papers; violet, green, and intermediate (which usually looks greenish but is actually a violet paper). Besides a direct comparison, the best way to be sure of which paper it is is actually by the vignette. Although Scott lists both as being black, the green paper vignettes are actually sepia. And they tend to have a shadow on the reverse as well. With the intermediate papers, the vignette is also black. And they glow violet under UV, whereas the green paper glows bright green. Which is why they are considered violet papers, even when they look greenish to the naked eye.