Try printing a "base" all by itself. This is to see what the color on the shirt is when cured.
Depending, you may need to add the barest amount of black to darken it up.
Here with plastisol, we take a very soft base - Primer Clear Ultra soft - and add about .5%, yes 1/2 of a percent of C3 system black to darken it up. So, with 99.5 grams of base we would add .5 grams of black.
Depending we will sometimes go even less depending on shirt and shirt color.