Could you advise what setting you are choosing at export, file type and colour space. e.g jpeg / sRGB, Adobe RGB, Pro Photo RGB?
What application are you using to view the exported file?
Is your monitor calibrated and profiled using a hardware calibrating device?
Some info to help is available How to manage color in Lightroom .
Mac or Windows? What version?
What software are you using to view the exported JPG?