If you use a 4K or HD display that is not physically very large (a small monitor or a laptop), it is often difficult to see the vertices in Edit Mode. This is easily fixed in the Blender Preferences pull-down but is quite hard to find:
Change this pixel value to a higher value (about double the pixel size of the default).
By the way…
I suggest you uncheck Auto-Save Preferences. The reason is that you don’t always want to save experimental changes. With Auto-Save Preferences unchecked, the bottom of the Blender Preferences window changes to a Save Preferences button which gains a warning asterisk if there are unsaved changes:
Now return to Blender, select an object and go into Edit Mode 
.
.Check the size of your vertices and modify as necessary by repeating this procedure.
How do I change the colour of the Selected Vertices?
Go through the same procedure as above but instead of scrolling past all the colour bars, stop here to change the colour:
In the same way, the colour of any element can be changed.
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