Dell Inspiron i5759 HDMI horrible display on external HD monitor

Hello, I just purchased this i5759-8836SLV (Windows 10) laptop that produces a very poor display on an external HD monitor (HP 22VC) when connecting via the HDMI port. It has an integrated Intel Graphics 520 and an AMD Radeon R5 M335 (4GB) dedicated graphics card.

The contrast ratio is very poor and the colours are dull when comparing to the laptop screen, with both displays set to 1920 x 1080 resolution.

I have switched HDMI cables and even monitors, with the same results. When I attach the same monitor to a different Dell laptop, the display works just fine. The image is very crisp and the colours are very bright and default factory setiings.

I have downloaded and installed the latest drivers, tried adjusting both monitor and graphics software settings without much success, the display still doesn't look as sharp and bright.

I have tried explaining the issue to Dell tech support, but without much success. The believe it is a monitor issue, as the laptop's built in display is working fine.