Defense Grid

Having found out the specific health values of the aliens courtesy of a GameFAQs user (who presumably asked for them here), I am left with the other criteria missing, how the aliens' health increases per wave. How exactly does this work? Do the aliens increase in health x % per wave in the level, or x % per wave only in the waves they appear? Or is it a fixed % depending on what the wave number is? Does it differ for each level? (Other than the number of waves involved), and crucially, what is the change? Or is it as simple as colour dictates health in discrete increments? Green=50, Green/Yellow=70 and so on... Thanks in advance