I bought a gradient at shop,it does not appear ingame.

You have to go to your deactivated inventory and activate it.

i did activate it,i activated both my force and gradient,gradient did not appear.
-----
Oh,i restarted my computer,it appeared

Next time, type /dl [Your_username], wait for it to say "Download Complete" in the chatlines, and then type /lp 0 [Your_username].

You can either do that or just play a few games in multiplayer, in which your customs would be downloaded automatically.