Making your own gesso may not be for everyone. If you can say what you want to say on an acrylic primed canvas board that's fine. For many painters it's hard enough finding to time to paint let alone prepare materials, but if you can work with good commercial panels and canvases so much the better. If your skills, however, are at a level where commercial products are keeping you from fully expressing what you have to say then you may want to look into preparing your own materials. The ground is the foundation of the painting, whatever is painted on that support will be affected by its strength and quality. The story of the three little pigs, as every young artist knows, is really a parable about preparing canvases and panels.
When you come to the final stage of preparation, the final glue and tone, you are starting to create your painting. The color you choose for the tone is the first color choice of your painting.
Earth colors are the most common choice. They are inexpensive and give you a gentle but solid support. Here I used raw umber. It is a warm, quiet color that will not overwhelm whatever I put on top of it. Ivory black works in the same way but is a cooler tone. They are like your best friends. Comforting, supportive but not intrusive.
If raw umber and ivory black are your best friends than terra rosa is more like a spouse. All the good qualities of your best friend but more exciting. It is a very jazzy, sexy, rich tone that wants to be part of the painting. It can drag down light colors if they are applied too thinly, but it can liven up a painting if it is allowed to show through from time to time.
Now if terra rosa is like a spouse then thalo green would be your mistress. It is a daring and dangerous tone, one that should not be used without careful consideration. Thalos are attractive but very strong colors and could easily overpower your painting. You might think you have everything under control only to realize later that the thalo ground has infected every color you put on top and ruined your beautiful painting.
Uh oh, this is starting to sound a bit too much like pygmalion and galatea.....