Mitsubishi L75-A91 colors are breathing..Mostly white color..

This isn't an email, it is a post to an online self help website.

Get your money back, it is broken and needs professional diagnostics and repair.

https://www.cnet.com/products/mitsubishi-l75-a91/

The blink codes for this set are not well publicised.

https://www.google.com/search?safe=off&rlz=1C1QJDB_enCA643CA644&sxsrf=ALeKk03ufSbnHgzIGbkl_4L3A9xQFaxUqQ%3A1612136708789&ei=BEEXYIW_L4jY5gKgpLzoCQ&q=Mitsubishi+L75-a91+blink+codes

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did you go into the menu and check the brightness there?

other than that could be a main power board or the video board

I would start by changing the memory card.

Try a factory reset. If it do not help you, check and replace its main digital board.
There are two methods to reset TVs. The first is simple to do; a Hard Reset. The other is somewhat skilled; is a Factory Reset (System Reset). To make it a hard reset, just unplug the TV from AC mains wall socket, and re-plug it back after 15 minutes or so. If you do this by overnight is better. This procedure will make it a hard reset. If you want to make it a system reset [Factory Reset]; you have to enter its service mode option, and select the factory reset option. If you wish to get some details; check the site linked here. Pull up older posts. http://electronicshelponline.blogspot.com/
Service mode entry, adjust and exit procedure to many popular brand TVs are given. Never forget to exit the service mode, after all adjustments have been done.

Error code [66]. If you wish to get some details; check the site linked here. Viewing it in "Mosaic" will make surf easy.
http://electronicshelponline.blogspot.com/

if contrast etc not set incorrectly it may be a issue on the main board which processes all signal inside the set===a 37 inch might cost you more to fix than to replace.

NO ,its not the Lamp it is your Light Engine. Call UED for price of rebuilt one 1-800-648-6657.

Had the same problem with white glows. Followed the directions in this link and the white glows and color brilliance was fixed.

http://www.avsforum.com/avs-vb/showthread.php?t=1148792

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Flip reset switch, then retry b/w/color selector (or switch from ch. 3 to 4).