This guide contains the original vector graphics used for Grasshopper icons.
The files were written with Xara Designer Pro 6, but Xara is pretty good at file compatibility so you can probably open them on many versions.
You are free to use and modify these vector graphics for any project, document or webpage that is associated with Grasshopper. You do not need to credit me, though it is not allowed to pass the work off as your own without modifications.
There are no fast and hard rules when it comes to the graphics style of Grasshopper icons, but I suggest you try and mimic line-weights, contrast, saturation and arrow and point symbols when designing your own icons.
Note that all icons must be 24x24 pixels and most icons in the original set leave a 2-pixel empty border around all edges. All icons with such an empty border have a drop-shadow with the following properties:
Blur = 2 pixels Colour = black Transparency = 65 out of 255 (roughly 25%) Horizontal offset = 1 pixel to the right Vertical offset = 1 pixel downwards
I apply drop-shadows as a post-process effect in a pixel-editor, as Xara is not good at pixel effects on very small images.