Blue Pigment is a crafting ingredient that can be processed and found, but not placed into the world nor into a quickslot, since it cannot be consumed.
This will yield 4 Blue Pigments for 1 Blue Flower each.
You do not need to unlock any crafting recipes for processing materials in the Processor. Simply carry Blue Flowers in your inventory/bag or in any quickslot and activate a Processor that has been placed into the world by looking at it and clicking your right mouse button or typing "f" as the default key.
By checking your inventory window then, you will see that it has been temporarily been reorganized for the Processor (only as long as the Processor window is open). The topmost section will be labelled "Processable", and by hovering with your mouse button over the icons listed, you will be shown what these items, blocks, materials etc. can be processed into.
This list will not include materials nor items that are stored in a storage container or placed nearby. You will have to move them into your inventory or quickbar.
Each Processor can be filled with 21 stacks of items (or materials) in its queue to be processed. If you hold down the "Sprint" key (Left Shift by default), you can process 5 times as many materials at once, just like in the Crafting Menu.
It will take some time for each material to be processed - both the time that one item(-stack) and all of them in the queue will take to be done is shown in the Processor window beforehand.
Blue Flowers can be plucked from nearly every pine-like Elderwood-tree and over time they slowly "regrow" on Elderwood Leaves too, even on Snowy Elderwood Leaves. They do not require any Power Cells to be harvested.
Blue Flowers can also be collected in significant amounts from Wood Treasure Chests that spawn on the surface and on surface layer blocks only at ingame-nights in complete darkness. To multiply Blue Flowers, it is even easier though to simply place blocks of Blue Flowers and pick them up repeatedly, which will occasionally yield additional Flower blocks.
Blue Pigment is an ingredient in the following recipes:
Creating or finding Blue Pigment is one of the unlocking requirements for the crafting recipe for Blue Concrete and other crafting recipes.