Darwinbots allows you to define custom variables at the start of your DNA that work exactly like sysvars in syntax.
At the start of your DNA, add
def varname number
Where varname is the name you want to attach to your label (variable) and number is the number you want to associate with this label.
For instance, to add a custom variable to store color, add
def color 50
You can now address *.color and .color within your DNA and the program will understand what you mean.
Note that this also works to create constants. For instance,
def myidcode 12566
will allow you to address .myidcode as a number, allowing you to quickly modify constants (in this case conspecific recognition probably) in your DNA code.