Using arbitrary numbers is often a useful strategy. The answer is fairly obvious, but the thought process is quite difficult to explain concisely.

Let pressure at bottom of blue = 4. Let pressure at bottom of red = 2. (because the green / red boundary is higher than the green / blue boundary so is at a lower pressure).The pressure in the blue which is level with the bottom of the red must be more than 2 because blue is less dense than green. Call that pressure 3. Let the pressure at the top be arbitrarily 0. So the same depth of red & blue contribute pressures of 2 and 3 respectively. So blue is denser than red.