how would you improve the buttons on the top of the screen? To grab attention of the user I tried to change a bit their color (they are dark blue instead of black), but I think that they are not coherent with the rest of the screen.
Generally, circles are used to show information (think social media profile pics); we see them less as buttons.
Try making the buttons rounded rectangles. I don't think coloring the icons necessarily helps make them more discoverable, and color might compete with what the user is trying to do visually on the canvas. Monochrome might be the way to go.
It all depends on the product strategy
if the target is to be an advanced graphic processing program it's worth thinking about the menu comprehensively and holistic.
Or put the interface elements on the left side of the canvas with the addition of a text / description of what they are doing
I agree with Stacy H's answer.
I would like to add that placing those buttons at the top and center of the screen is placing them in possibly the hardest place to access. The Users hand and arm will often cover the actual content while accessing those buttons and the User must reach for the buttons. Left(start) and/or right(end) sides or underneath the canvas would achieve easier access.
The placement of the EditText underneath is odd too, as that is prime realestate for usable widgets and will be covered up by a soft input keyboard. It seems to be the least sensible place for the EditText.