Red color lost in my tab 10.5
If the test is not displaying any red this is your LCD (all colors are created using 3 LED (light emitting Diodes) Red Green Blue (RGB)  Sadly your R is DEAD.  It might be something as simple as a loose correction which a technician with a test kit and some soldering could fix.

But I doubt you could do it yourself sorry to say.  Find a good computer repair shop near you.... Or contact Samsung and find an "authorized" repair shop if you are wonder warranty.

Good LUCK!