HP 510 - Manual (Page 175)

Screen contrast
You can adjust the screen contrast of the front panel to best suit the ambient lighting conditions at your location.
The contrast can be varied from 0% to 100% in 5% increments. The default setting is 50% and is suitable for most
situations.
To adjust the screen contrast:
1. Select the Front Panel > Contrast option from the Set-up menu.
NOTE: Any value below 20% shows a blank screen and any value over 80% shows a black screen.
2. Scroll to the required value and press Enter.