How does marijuana make your eyes go red?

How do clear eyes make them go white again?

How come they stay red for a bit afterwards like a couple of days?

If you're talking about the whites of your eyes going red, then it's simply the dilation of the capillaries in the sclera (the white of your eyes). Anything that reduces this redness is simply reversing that effect.

the weed works as a rather powerfull vaso dilator, and that in turn has a profound effect on blood pressure, maybe you may have noticed your heart feeling particularly odd to the point of being very noticable whilst being "stoned", some can actualy feel it beet that strongly it causes them to panic.

the dilation effect is as Glider said. the "Clear eye" will contain a local anti-inflamatory ingregient that will reduce this effect.

as for the long term red-eye, I can only assume it takes some time for the drug to get out of your system, I can only speculate at that part of it