The brush’s color:
Using the
Free Transform selection, try to stretch out the spot horizontally and turn it over the same way shown next picture.
Use the same method described above to represent a white spot.
The layer containing the white spot needs the parameters from below.
Blending mode-Overlay 
Make a copy of the layer containing the white spot and select
Free Transform option to make the copy smaller and change the layer’s parameter also with that one from below:
Blending mode-Normal 
Next we have to choose the
Ellipse Tool (U) and represent the primary layer of a bubble to be later.
The layer’s parameters:
Fill 0%
Blending Options>Inner Shadow
Now it’s time to draw a highlight on the made bubble, applying the same
Ellipse Tool (U).
The layer’s parameters:
Fill 0%
Blending Options>Gradient Overlay 
Gradient’s parameters: 
