Orange Bloodroot is an item used to create Orange Dye. It can be found in the UndergroundBiome, hanging from the ceiling. They are fairly rare to find, however they will be even more difficult to find without a light source and a keen eye for them.
They can also be found hanging from regular dirt blocks above ground on Mobile, seemingly more frequently than underground.
Using Spelunker Potion can be a great help in spotting these plants in a dimly lit underground.