A color so pale, it's almost not there.
Tertiary colors are the colors used to create the illusion of a color. They are created by mixing a primary color with its complement and a secondary color. In the case of pale green, it's made by mixing a tiny bit of blue with a lot of yellow.
Here's a chart to help you remember:
| Pale Green | Yellow + Blue (1:10,000) |
Pale Blue might be more your speed.