Why do some decorated weps with effects show as unusual, and others not?

[duckDecoy]

Lets say I search for rocket launchers with isotope and prof KS

https://backpack.tf/classifieds?item=Rocket+Launcher&tradable=1&craftable=1&killstreak_tier=3&particle=702

 

Some of the images in the retrieved listings are full purple background indicating unusual, and the rest are not.  If I further filter by Quality it confirms that some of the listings are classified as unusual, and the rest are classified as decorated.

 

Is there a difference?  Is there an unusual isotope RL and also a not unusual isotope RL?

 

Cheers

[Phink]

pretty sure that the ones that came from war paints dont appear with blue background and the ones that came straight from cases do. 

[Phink]

15 minutes ago, Phink said:

pretty sure that the ones that came from war paints dont appear with blue background and the ones that came straight from cases do. 

or not. doesnt seem like thats it eather

[TF2Scourge]

The ones that show as unusual were unboxed before the applyable War paints were introduced to the game.

Decorated weapon ones are ones that came from War paints/ unboxed after War Paints were added.

There is no difference in look, but some people will pay more/less for this slight difference.