Why does laser beam might appear blue and another laser beam might appear red?

One thing about a laser is that the light it puts out is all one single sharp
color (wavelength) of light with no other wavelengths mixed in with it. 
That wavelength is a different one for the different kinds of material
that are used to do the "lasing" ... generating the light.  There are a
couple of different wavelengths of infrared lasers, and several different
types of lasers in the visible range.

D. Each laser beam is made up of one specific wavelength of light.

Explanation: Lasers are in one specific color because it is made up of one specific wavelength of light. So the blue wavelength is blue and the red wavelength is red.