how to sequence parameters in javascript functions

how to sequence parameters in javascript functions

I was writing a code in javascript.
colorMixer = function (redIntensity, blueIntensity, greenIntensity)
{
// mix color
}
colorMixer(10, 8, 7) // means red = 10, blue = 8, green = 7
colorMixer(10, 8) // means red = 10, blue = 8
Question: How to specify red = 10, green = 8, and no value for blue (i
dont intend 0 value for blue) I want scene where value for blue is unknown
and DONT want to provide any value for blue.