Symbol Stainer Tool

Click or drag over the symbol instances you want to stain with the colorization color. ...

A symbol set is a group of symbol instances that you create with the Symbol Sprayer tool. You can create mixed sets of symbol instances by using the Symbol Sprayer tool with one symbol and then using it again with another symbol.

Staining a symbol instance changes the hue toward the tint color, while preserving the original luminosity. (It works in the same way as the Tints and Shades colorization method of tinting brushes.)


SOURCE:
https://helpx.adobe.com/illustrator/using/symbolism-tools-symbol-sets.html