one old test turned grey?

Lilli ā€¢ Jesus ā¤ Mommy 2019 šŸ‘ŖšŸ’• Married 2017 šŸ’‘ Jax, Florida šŸ¦€

i know these are all invalid and im definitely not going back to see if I'm pregnant BUT my old tests have never turned grey? does that mean it was a

dud? or what? BOTH ARE OVER A WEEK OLD. the grey one turned grey after about 4 days? so I'm just like.. hmm?