Do tests fade after a few hours?

[RubyB]

Hello,

First time here and just after a bit of advice. I had my first ever positive OPK yesterday (on christmas day!!) and the line was very clearly darker than the control. However when I looked at the strip a few hours later it had faded a bit and no longer looked as dark. Just wanted to check that this was normal? I think I'm in such disbelief that I've finally got a positive that I'm being paranoid

Many thanks

 

[PeanutButter]

Yes it's normal when they dry x