I usually make layers for 2D blue curves blue, for blueprints. Lately, I’ve taken to using a variation of Prussian Blue, which was involved with traditional Cyanotype blueprint making.
Wikipedia states that the RGB color coordinates are: 0, 49, 83
Working with Rhino3d’s default color scheme, I use: 0, 76, 128
…which is the same shade but with a brighter. Only 2 values need to be typed.
It might be handy for the internet/Photoshop crowd, if people could type in a hex RGB value into the Rhino color coordinate box.