Why do glasses have a greenish reflection? I've been playing around with my glasses, and noticed that they often have a greenish-blue reflection, like the one in the picture below.

Cameras have a similar glint, although less noticeable.  Why does this happen?
 A: The lens have an anti-reflecting coating on them.
The process of putting the coating on is called blooming.

The thickness of the coating is $t=\dfrac{\lambda}{4 n_1}$ where $n_1$ is the refractive index of the coating which is between that of air and the glass of which the lens is made.  
For a wavelength $\lambda$ the reflected rays $A$ and $B$ are exactly out of phase and so they cancel out and there is no reflection of the light.
However this condition is only satisfied for one wavelength which is usually chosen to be mid-spectrum green - $550\, \rm nm$.
The optimum refractive index for the coating is $\sqrt n _{glass}$.  
The condition given for destructive interference is for normal incidence rays.
If the angle of refraction in the coating is $\theta$ the path difference between rays $A$ and $B$ is increased by a factor $\sec \theta$ so the loner wavelength towards the red end of the spectrum are not reflected as much as those at the blue violet end so a bloomed lens looks blue-violet as shown below. 
 
This can be improved by having multiple coatings on the lens which then eliminates more wavelengths and so there is less reflected light.  
This diagram from the HyperPhysics website Anti-reflecting coatings illustrates the progression of increased number of coatings. 
 
This graph indicates the sort of improvements which can be made noting that the refractive index of the single layer coating is not ideal $(\ne \sqrt n_{\rm glass})$ and so the reflectance does not go down to zero.

There is much less light reflected from the lenses and the colour of the lenses by reflected light is changed again.
Such coatings produced at an opticians usually have a very faint residual colour which is usually green or blue and that is probably the reason for the colouration of your lenses.  
