Desktop image keeps reverting to blue when programs/folders are clicked

hi,

afternoon browsing on website , wouldn't let me view important information because didn't have plug-in. after downloading plug-in noticed desktop image on macbook pro randomly turn blue. i've re-set on 15 times, when open programs/click on reverts blue..

when go system preferences , click on 'desktop , screensaver' shows desktop image in small box photo i’ve selected, screen still blue.

know how fix this? has never happened before, , it's starting become rather irritating.

 

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