Why is there a blue highlight behind some Pokemon??

[Shootme]

So I've been collecting for a while and I noticed that's some pokemon have a blue highlight behind them and other don't. Does any one else notice this??

 

[Alanhd]

These are Pokemon that you have caught recently, I think in the last 24 hrs.

 

[Shootme]

thanks, and here i was hoping i stumbled on something cool, NOPE! HA

 

[Morty2264]

Haha, I had noticed this too! I guess this lays my suspicions to rest! LOOL.