Hello! You're right to notice. I do not know what's the beer mat, but most likely that his "touch-up" in the yellow color is used Fog color, other than white, as well as the Fog multiplier, different from zero.
The essence of the Fog color parameter to create the effect of color "mist" in transparent and translucent materials.
Color determines the color of fog pattern the Fog color . The density of the fog color enhances the Fog multiplier . Moreover, the fog density depends on the thickness of the object itself. Than it is thicker, the more dense the fog and vice versa.
Of course, the thickness of the object in the scene is measured in units of scenes of system, and the more the object is, the thicker it is considered. It turns out that the material c Fog color + Fog multiplier, configured to be slightly yellowish in the circle with a diameter of ~ 100 mm, with an increase of the mug, make it dark and opaque. Then your light beer will look like El .
You do not change the size of the circles, but you change the system units, while leaving the original size of the cup, not by scaling it to the desired number of times (as many how many new different system units from baseline). Here on this liquid in your mug is darker, the lighter 🙂