Top: You usually play with teleport, so you need yellow trinket in order to have some control over your teleporting spots.
Jungler: You want to know when you are spotted, so you need to know if an enemy ward saw you, delete it and run away before being caught. So you need a red trinket.
Adc: You are weak as F, you dont want to put your ass remotely close to an unwarded zone. So you use blue trinket to ward from afar.
Support: You have your sighstone, so you can provide vision, but you want to negate your enemy's vision too and make your opponent support's wards useless. So you need a red trinket.
Midlaner: whatever you feel more useful in this game. But, remember to pink the river and to yellow the same side near your opponent's tower. Since that side is visible, probably you will want to use yellow during a big part of the game.