Last year I think the back-light started breaking down - I see big square sections where the colors are less bright and purplish. The display seems to have a grid of 4x2 of these individual regions.
And the remote buttons are getting harder to press too (it's not the battery). I had remotes which worked for 12 years, this one is barely 5 years old.
I had my TV (similar to yours) fixed by replacing those bars, check with a TV repair shop in your area.
I will warn you however that it's quite an involved process - I know a fair few people who have managed to crack their LCDs or rip ribbon cables in the process of trying to fix backlights.
Unfortunately it seems that backlight issues are becoming more and more common - especially as most sets have a "Dynamic" mode or similar which sets the backlights to full brightness and drastically shortens their lives.