VIS: let scatter plots obey mpl color scheme (#3338)

Closes #3338.

Fixes the remaining plot functions that don't follow the matplotlib style (functions based on scatter plots).

Rationale:
- set the color keyword `c` to default one defined in matplotlibs rcParams if `c` was not specified by the user (because `c='b'` is harcoded in matplotlib ``scatter`` method).
- the `color` keyword is not checked because, if specified by the user, it already is given preference by matplotlib over `c` if both are given.

There is a new PR on scatter based plotting methods (#4930), but I suppose that it can be handled in that PR to ensure this new plotting method also follows this approach?