Note: Something similar was criticized for the desktop version (cf. T2768).

How to reproduce:
E.g. try to save a change in settings
or compose an email
or click on "option" in the "mail" area

Actual results:
All buttons are black (they turn blue only when clicked on).

Expected/Desired results:
Colors of buttons should be adapted to kind of action AND then used consistently throughout the program.

This means:
All buttons which are black at the moment AND which stand for the successful end of an action (e.g. "Save", "Send") should be green (because green stands for: "success"/"everything ok").
Conversely, all buttons which are black AND stand for ending/breaking off an action (e.g. "Cancel") should be red (because red stands for: "watch out"/"do you really want to end this?").

Note: As far as composing an email is concerned, the question is if both buttons should be made green because actually "Save" as well as "Send" do both stand for "successful ends of an action". It might thus be senseful to make both buttons green, but make the "Send" button stand out a bit more - e.g. simply by making it bigger.

Note: These comments on "appropriate" use of colors are not valid for "simple actions" such as "edit"!