>>4132105trichrome is a proces where you take three photos of the same subject with different color filters, those being red green and blue. because these filters block all light except for their respective colors, you are left with a red value, a blue value and a green one. you overlap these in photoshop, assign them all the correct color and wham, you have a true color photograph from black and white film.
this video explains it very well
https://youtu.be/BaqgmnoK_Us 