I have a problem with my laptop's screen. The colors seem washed-out. I am pretty sure that the problem lies in the LCD screen but I would like your opinion.
1)I tried connecting an external monitor with both VGA and HDMI and the external monitor works fine
2)I replaced the lcd cable but the problem remains
You've pretty much done all the test needed to confirm that it's the display itself that has the problem. One last troubleshooting step would be to uninstall/reinstall the graphics card driver but if that will not work the only solution would be to replace the display itself.