Working on Recipes Folders

I am working on a project to create recipe folders for my children to learn to cook.

How do I make it easy for my children to locate the recipe they are looking for? 

I can use colour codes like this which I can indicate on the envelope.



A 162x229mm envelope is large enough to hold A5 paper.  So, this is the size I need to print my recipes on if I want to fit them inside one neatly.

Looking at this envelope sizes, maybe it is a good idea to consider using DL format which is of  size 110x220mm.  Maybe, I should work on the recipes first before I decide what size folders I should create.